The short answer

There are indeed some examples of great scientists who accepted one form or another of creationism, especially if one counts deism as a form of creationism. However:

• Most examples of such scientists are drawn from early in the history of evolutionary theory, or even before Darwin. The closer one gets to modern times, the fewer examples one sees.
• Some of the examples creationists tend to cite rejected a young earth, a worldwide Flood, a god who interacts with the world after the initial creation, and many other aspects of Genesis that contemporary creationists tend to accept.
• The scientific accomplishments of some creationists does not necessarily mean that they behave like scientists when considering evolution.

The longer answer

If one considers deism (God starts up the universe, then leaves it alone) to be a variety of creationism, then it is true that many great scientists in the past were creationists of one form or another. If one confines creationism to those who believe that God directly created all life around 6,000 years ago, then fewer great scientists of the past qualify. Either way, however, nothing helpful follows for modern creationists.

Most examples are drawn from early in the history of evolutionary theory, or even before Darwin

The scientists creationists cite become scarce as the evidence for evolution mounts up. For instance, one creationist publication (Morris 1982) claims thirty-five “great scientists” for creationism. Of these men, thirteen (Bacon, Kepler, Boyle, Pascal, Steno, Da Vinci, Ray, Linnaeus, Woodward, Newton, W. Herschel, Davy, and Cuvier) died before the publication of On the Origin of Species in 1859. Fourteen more (Pasteur, Babbage, Maxwell, Faraday, Mendel, Agassiz, Simpson, Maury, Riemann, Brewster, Joule, J. Herschel, Henry, and Morse) died before 1900. Of the eight who lived into the 20th century (Lister, Kelvin, Fabre, Stokes, Virchow, Rayleigh, Ramsay, and Fleming), only one (Fleming) lived long enough to see the advent of the modern synthesis of evolution. Not a single person on the list was still alive when the structure of DNA was discovered in 1953. This trend reflects how Darwin’s key contributions to biology, and the steadily mounting evidence for evolution thereafter, caused the scientific consensus to shift from creationism to evolution, and eventually relegated creationism to its proper status as a pseudoscience.

Thus, the fact that it was at one time possible for an informed and unbiased scientist to be a creationist, does not establish that it continues to be possible today. In the same way, the fact that great scientists like Newton and Boyle believed in alchemy does not show that it still is possible today for an informed and unbiased scientist to accept alchemy (with mainstream chemists presumably being the vanguard of a grand materialist conspiracy against god, truth, and morality).

Not all of the examples above are friendly to creationists who cite them

Not all of the scientists in the list above would make comfortable allies for contemporary creationists. Here is just a handful of examples:

1. Agassiz rejected Genesis: “Agassiz was a religious freethinker like Darwin… When pressed, he would say that Genesis was wrong and the Flood story was just watered-down ice-age science” (Desmond and Moore 2009: 232).

2. Davy may not have believed in a creator at all, and W. Herschel was both vaguely deist and manifestly not a young-Earther:

Whatever he said in his famous lectures, Davy’s poetry and his posthumous writings, such as Consolations in Travel, suggested a kind of science mysticism that certainly precluded a Christian God, and possibly even any kind of Creator at all. Others, like William Herschel, had been content to rely on an instinctive, perhaps deliberately unexamined, belief in a benign Creator somewhere distantly behind the great unfolding scheme of nature. Though in Herschel’s case, his own observations had shown how extremely—appallingly—distant, both in time and space, that Creator must be. (Holmes 2008: Chapter 10)

3. Babbage rejected a six-day creation and a young Earth. He believed that spontaneous creation events separated by long periods of time were built by God into the laws of nature:

I added, however, that [analytical engines programmed to suddenly switch to a different set of laws after a fixed period of time] offered a striking parallel with, although at immeasurable distance from, the successive creations of animal life, as developed by the vast epochs of geological time.(Babbage 1864:389)

In what sense creationists are not real scientists

The debate about whether or not creationists can count as real scientists (and the point that creationists miss when they complain that evolutionists just dogmatically define science as naturalism) centers not so much upon the question of what creationists believe about the world, as upon the manner in which they approach evidence. The issue scientists have with creationists is not, per se, that creationists believe the earth to be 6,000 years old or what have you; if that were all there were to creationism, there would be no problem at all, because scientists would be able to convince them of the actual 4.6 billion-year age of the earth by presenting evidence. The problem is that most creationists seem not to be open at all: they appear have decided in advance, on the basis of their personal interpretation of whichever religious texts they accept, that such-and-such must be the case about the world, and that any evidence to the contrary must be rejected. Creationist Kurt P. Wise is representative of this mentality—with admirable candor, he writes,

Although there are scientific reasons for accepting a young earth, I am a young-age creationist because that is my understanding of the Scripture. As I shared with my professors years ago when I was in college, if all the evidence in the universe turned against creationism, I would be the first to admit it, but I would still be a creationist because that is what the Word of God seems to indicate. (Ashton 2000: 355)

That is what scientists have in mind when they say that creationists, even those who publish respectable scientific work outside of the context of creationism, are not real scientists.

Those who say that modern creationists are not real scientists rarely mean by this that creationists cannot do good scientific research when working on issues unrelated to those against which they have an ideological bias: in such cases, creationists use the same methods and standards as mainstream scientists. Likewise, an aficionado of power crystals can still be a good engineer, and a believer in astrology can still be a good doctor, as long as they do not allow those beliefs to guide their practice. Again, there is nothing strange about a creationist being able to do normal, even brilliant, scientific research when they behave like other scientists. It is just that when it comes to areas like evolutionary biology, religious bias keeps the same creationists, however well-intentioned, from using the same methods and standards they use in their respectable work. This should not be surprising, as it is ubiquitous in life: for any crackpot idea you can think of, you can find someone with an otherwise excellent mind who believes in it. But that is one reason why it is so crucial for scientific work to be peer-reviewed in mainstream journals: bringing the collective attention of mainstream scientists to bear upon an idea or report is one of the best ways to control for unnoticed personal biases. Likewise, an attempt to bypass mainstream peer review and appeal instead directly to legislators and the masses, as creationists do, is as sure a sign of bias and crackpottery as one can ask for.

References

Babbage C. 1864. Passages from the Life of a Philosopher. London: Longman, Green, Longman, Roberts & Green.

Desmond A and Moore J. 2009. Darwin’s Sacred Cause. Boston: Houghton Mifflin Harcourt.

Holmes R. 2008. The Age of Wonder. New York: HarperCollins. Kindle edition.

Morris HM. 1982. Bible-believing scientists of the past. Impact No. 103.

Ashton JF. 2000. In Six Days. Green Forest, AR: Master Books.