Can only Zerg units use Nydus Worms?
Currently you can have all races be able to load up in the Nydus Worms, as long as they are your ally. This is of course subject to balance. You should have saw the face of our community team guys when we played a 2vs2 and a Nydus Worm busted up inside his base, and both Hydralisks and Zealots came charging out.