While I think there exists a level at which mainstream religious faith is inimical to epistemic rationality, I also think it's most likely a pretty advanced level, higher than most if not all of the regulars here have attained. (Note however that people can and do give up religion on grounds of rationality before hitting that level.) It's certainly possible to make substantial contributions to the advancement of human rationality in its present state while also being a theist, and that was still truer a few hundred years ago when the foundations of the art were being laid.

That being said, there's also a distinction to be made between esteemed rationalists and esteemed scientists or mathematicians whose work contributed indirectly to LW-method rationality. Of the people that worked on the early foundations of statistics, Laplace is the only one I can think of offhand that strikes me as having had strong public commitments to rationality in this site's usual sense.