Well, my plan was to focus on fictional Nazis (though a lot of them would be based on real life fugitives, like Mengele, Eichmann, and Cukurs). I wouldn't feel right casting real life monsters in a game, even as villains. Besides, I'd like a bit of wiggle room for the story I have in mind, which original characters are better for.

Hope you're still interested even with this in mind.