If I liked the artist before I found out who they really are, I can still like their art. If I found out the artist was a piece of shit before I discovered there art, I can never look at their art in a good light.
If I had seen this painting not didn't know who the artist was, I would say it's very nice and well done... But knowing it's Hitler, I can't appreciate it.
Using anything Holocaust related as an example is a little far reaching, but rape is torture.