Being a good boss doesn't make you a good person. Being a guiding force in a genocide isn't just "unethical". These two aspects are so radically out of scale morally that it shouldn't be complicated at all.

I get pondering the morality of Syril or Luthien, but there really shouldn't be any question about Partagaz. A "nice" Nazi is still a Nazi.

Hitler was pretty animal friendly and, for all we know, in a fairly loving relationship with Eva Braun. Pretty much no real person is evil to everyone, always and in any situation. That doesn't make Hitler any less of a bad person. I would even argue it makes him more evil: He knows how to treat living beings with respect, he just thinks a majority of humanity isn't worth his respect.

It's not about what the person seems like in day to day life. It's about the actions one takes. There are some actions no good person would take.