We had actually baked in support for NaturalPoint's TrackIR product back in the early development of Rise but the support was never carried over to game client 2.0 as we had no active players (that we knew about at least) that used head tracking.
The other day I was talking to a player and he mentioned head tracker support. Literally within 48 hours we had released support for head trackers on Steam. And it is a step in the right direction for our VR initiative!
The user in question is using OpenTrack which is a free software that you can use to configure and "shape" your existing head tracker, VR headset, or FaceTrackNoIR.
If you don't have a head tracker peripheral but would like to use one in Rise:
TrackIR 5 (highly recommend)
DELANCLiP Gamer (currently on sale)
TrackHat