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.
The whole POINT is to let in talented people who are more attractive than a college grad. Having such a pool of people _inside the US_ is a huge competitive advantage over countries with strict immigration. What in the world keeps American engineering salaries so high if not available talent pool?
If you want them in the talent pool here, give them a green card, not a temporary visa, or at least a temporary visa with a clear path it citizenship. Say, after the first year or two it converts to a green card instead of just getting an extension. Also, if they are more attractive than a college grad, why are they only getting about the same pay as a college grad?