Well, we shall no doubt see in time. However, I feel I prefer to trust the word of Revan's greatest teacher, his first and his last, who formed him into what he was, and someone who could see thousands of years into the future (even predicting the death of the Mandalorians), as well as who predictions almost always came true, over some Jedi Master who is recording these things as the Jedi see it 300 years after the events.
Daniel Erickson, lead writer for BioWare Austin, stated however, that when Revan and Malak met the Sith Emperor, he did indeed turn them to the dark side and used them as pawns to conquer the galaxy, or at least establish a hold in the galaxy for when the Sith Empire would return. Seems that BioWare prefer to keep characters more black and white, over grey, complex, and infinitely more interesting.