I don't really care how he chose the animals so much as how the characters actually act. I don't think you can judge the choice of characters just based on how he chose what animal for who. Then you're pretty much limited to assuming it's a stereotype because you're looking for what the animals represent to people, which has already been defined by you as a stereotype.

That said, I usually dislike Nazi stories because they end up being heavily moralistic, but not all of them are, and often less so for people who were actually there than people who write about it with no experience of the individual nuances and hypocrisies and whatnot.