It includes the source code for the expansion pack game dll (in d3xp). You'll still need the original RoE assets (when I went to install them on Windows, the installer crapped out because I wasn't on Windows 2000 or XP, but you can just copy them from a directory on the CD- they're in a d3xp directory or something like that).
The idtech4 source code release does not include any game data whatsoever (only the game engine source code), so the short answer to your question is "no".
The slightly longer and more correct answer is the source release contains the game engine source and the Doom 3 and RoE game DLL source. The Doom 3/RoE game data is still required.
