Some Vtubers do use VR headsets (Mirai Akari does, dunno know for how much of her stuff is with it but she has to use it for VRchat). I can’t say how many but VR headsets offer the best option for motion tracking.

I, mean, I could get a kinect too and that’d work as well. And, Facerig only works on the face as far as I was aware while a lot of Vtubers have full body motion.