I can really sympathize – I avoid cameras wherever I can ;)
As far as I know NaturalPoint imposes pretty draconic measures upon the licensees of their API. If you implement TrackIR in your game, no other tracking API may be implemented (granting them a monopoly on a per-game basis), the API itself is encrypted and all that. Not a very open or friendly licensing model.
But, for the legalities, there might be a loophole – you cannot offer it working right out of the box in a commercial product because they might sue you but let’s say there is a module API in VorpX itself that will allow let’s say tracking i/o, the open source community will find a way to make a free module addon to VorpX that you are neither have to do the work for and are not legally responsible. Just make it open enough for a solution to be integrated into your product by some fellow enthusiasts if you know what I mean. ^^