I recall watching a Twitch.TV streamer a couple weeks ago playing the new PC version
of GTA5 and he was using TrackIR.
I have not idea how he implemented this. No details. Just know he was using it and it was working, though somewhat glitchy.
I"m guessing he used mouselook mapping mode for TrackIR.
IT was ClassyPax on Twitch.
http://www.twitch.tv/classypax/profile
He mainly is into air sims.