Firstly if the GM says that undead are evil *in his game* there isn't much you can do about it.

But in my opinion, you need true sapience to be evil. Unintelligent undead are Neutral. Yes, I know that the Create Undead spell has the Evil descriptor. But neither the Negative Plane nor Negative Energy is evil. I don't think the spell should have the Evil descriptor. I see unintelligent undead as not much more then really conveniently shaped animated objects.