People with apparently irrational religious views have had major insights into technical areas of philosophy and to the theory of rationality:

Thomas Bayes Robert Aumann Saul Kripke Hilary Putnam

I'm sure there are others, but these are the best known examples. Putnam was also a Maoist for a while. A number of top German scientists worked for the Nazis, having seen their Jewish colleagues chased out of their university positions.