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.
3.0 followed this- but 3.5 dropped it. That said, in the 3.5 Draconomicon book skeletal dragons and zombie dragons are neutral, unlike dragon zombies and dragon skeletons from MM, which are NE.
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