EDTracker Pro works natively within Microsoft FSX (Flight Simulator 10) - the game pics it up as a joystick which can then be mapped to the view axes. EDTracker Pro user, Roger Hopkins, kindly sent in this guide on setting up EDTracker Pro with FSX. Many thanks, Roger!

Of course, there's nothing stopping you using the Opentrack approach as well, if for some reason you prefer it, to simulate other head tracking protocols.