Back then it was a major pain to get the Dark Mod to install and properly operate on Linux. This was due to the game having had *very* specific ideas on where to install stuff, and the defaults where the game expected its media did not fit my file system structure (e.g., all my games are at /mnt/data/games, not /usr/local/). Sadly, symbolic links did not work at all. Also to select a campaign one would have to select it ingame (which would apparently copy some files around?) and then restart the game, which would only work spuriously etc.
I think I read back in the days that the open source engine release would offer you the opportunity to rework the whole file system stuff to work "as expected" (unzip game and/or new campaigns wherevery you want, start, play). Any chance this already happened?