A lot of today's very renown artists, authors and philosophers were convicted in crimes. Oscar Wilde was imprisoned for homosexuality, Egon Schiller for some moral sexual thing, Socrates was sentenced to death for corrupting the youth and so on. There are a whole bunch of contemporary musicians that wins grammys and other music awards while being convicted for drug use, DUI, sexual assault, etc.
Being an artist doesn't mean you have to live a more moral life then others.
He got an awared for making a good movie, not for being a good person. If this was the "honorary good person prize" then I would have seen a problem with him winning, but since the movie is very good and deserve the award, I can't see a problem.