Well, Hitler's paintings weren't the best (I've seen at least one). But since you mention Nazi Germany, it is interesting to note the work of Leni Riefenstahl. A great, innovative documentarian? Undoubtedly. But also complicit in Nazi Germany, to my mind. I admire her craft, but obviously loathe the propaganda she chose to produce with her talents.

By contrast, Woody Allen is someone whose films I greatly enjoy, and I'm able to entirely disconnect them from his personal life (including Sleeper, Annie Hall, and Manhattan). I feel the same way about Roman Polanski's films. More on my thoughts on all this here, if you've not seen it and are interested. :)