In Unfinished Tales, it would seem that is true. But I agree with Corey that if you go by that story, Gandalf's going to Isengard when he gets the message from Radagast. Personally I think Saruman must have started out honest and earnestly began his studies of ringlore to figure out how to defeat Sauron. I think his studies corrupted him. The root of the problem for him was probably that the power of his voice made it possible for him to control others, and that could grow as he learned more - perhaps a hint of hubris.