As the FAQ mentions, The Dark Mod is primarily a toolset:
Our goal is to provide all of the textures, models, AI, and programming necessary to allow Fan Mission authors to create their own stories. We will be releasing some playable maps at the same time, both for fun and to demonstrate all the new features. Once the tools are released, we have plans to create our own campaign for release at a later date. We are all fans of stealth gaming, so we want to release the tools as quickly as we can so we can benefit from the creativity of mission authors out there!
Linux will be supported, as noted in this forum thread:
It seems you’re really asking about the editor, not the Mod itself, but just to be clear: Several of us already have the Dark Mod compiled and working under Linux. I even do all my mod development under Linux. There are a few caveats; the lightgem isn’t hooked up properly yet, for example; but we hope to have those ironed out before release.