Just doing some poking around looking for a linux 3D modeller. Stumbled across Moonlight 3D. Appears to be a free native Linux modeller, which also works in Window$. However, it appears to be in its infantcy. So documentation is light (non-existent), but you should be able to get in touch with the programmers to help come up with new stuff.
Btw, its also an animater as well. Hopefully, a file format or file importer/exporter can be implemented which can accomodate Nexuiz. Just throwing it out there.