All of those use the driver from Oculus which is what I will assume Carmack will be key in improving, along with the firmware running on the Rift. His experience with Armadillo will be directly applicable (and already has it seems) to aspects of real time head tracking that have a big impact on VR. I'm guessing the time to get the software in a more polished state just got shorter with him joining the team and it wouldn't surprise me to see a few new algorithms that noone else though of either.
"Just think of a computer as hardware you can program." -- Nigel de la Tierre