This is a good argument but IIRC Eldar and Tau don't use the warp. Not sure on Nids either. Eldar have the webway and Tau are warp innert and have their own system.Alright this seems like an epic project so I have to get my two cents in. Considering the literature on space hulks describing them as large conglomerates of vessels that have been smashed together in the warp maybe you could also add some alien features (orks, nids, eldar, tau) just to liven things up a bit. I mean these things are made of ships lost in the warp, right? It would kinda suck if only the Imperium got lost in Maelstrom...
Still Orks, and pre imperial races would be cool...then again i always think orks would be cool.