The creature rules on vermin say that they are immune to mind-effecting spells, but also that they breath, eat, and sleep. Why wouldn't sleep effect them? Spider brains, for example, are very different from humans so I can buy them being immune to most mental magic, but they do go through quiescent periods like pretty much all animals. Sleep would make a giant spider encounter I have planned somewhat easier for my PCs, if they happen to have it prepared.
Well, undead are so unnatural that their minds are entirely different or something. But meh. I'll figure it out.