No need for OpenTrack to do that. Can be enabled and configured in the vorpX menu directly by turning off the ‘X-Box Gamepad Override’ option and then enabling ‘Head Tracking as Gamepad’. Afterwards a few related secondary options appear in the menu, which may have to be adjusted per game.
Caveat: games usually filter gamepad input quite heavily, which makes head tracking emulating a gamepad feel quite laggy. General rule head tracking wise is: DirectVR or TrackIR head tracking (if available) > mouse emulation head tracking > gamepad emulation head tracking. So don’t use gamepad emulation head tracking unless absolutely necessary.