Nor would all the German actors who signed up for it.
I wouldn't even say that Nazis are demonized in the movie, although considering they were the scum of the Earth at that time, they'd pretty much have it coming if that was the case. But: The smartest, most educated and charismatic character in the film is actually a Nazi.
But regardless of that, it's hardly a film that is trying to be historically accurate anyway.
If anyone takes "Germans are awful people" as this film's message, they should have their brain checked.