The code isn't open source, and isn't GPL compatible (it would matter more for a distro than for us). It's not "open source" since you can't profit from it in any way. That means you couldn't include the source in a distro which is sold, for instance.
They basically just released the source code for educational/recreational purposes only. All of the code belongs to Volition, everything based on the code belongs to Volition, and profiting from the code in any way is a violation of the license that the code was released under.
As far as the data goes, Volition still has the copyrights on it, just not the distribution rights (as far as I know). So, technically, both Interplay and Volition are fully capable of suing you if you distribute the game data. I have a feeling that if Volition had the rights to do so, they would release the data for download, but they haven't. That may be the reason that they haven't sent out any C&D letters yet, but that could change at any time. Just FYI.