For anyone interested, I wrote a setup guide on The Dark Mod forums for getting the game running with Vorpx: http://forums.thedarkmod.com/topic/17501-oculus-rift-the-dark-mod-vorpx/
If you’re not aware, TDM is an extension of the Thief modding community. Specifically, it’s a Doom 3 total conversion mod that has gone standalone and is completely free. It’s a 1st person stealth game heavily inspired by Looking Glass Studios original Thief games. The game consists of fan-made missions, of which I believe there are over 100.