I did disable headtracking, but it didn’t change anything: If opentrack is running when vorpX starts, it complains about not being able to find a Rift. If I start vorpX first, and then opentrack, and then the game, vorpX will complain about not being able to connect to the Rift and the game will crash before opening it’s display.
Unfortunately, opentrack has to be started before the game runs, as it won’t see it otherwise.