I'm with you that I doubt there are GANs running in real time here, however I don't know see why they wouldn't be using similar models for offline static asset generation.

As far as scans go, it's much cheaper than you would imagine to get high quality face scans. Rigging them for animation is the real challenge, and I'd be really impressed if they were using GANs for rigging.

For state of the art in this space.. check this out: https://twitter.com/ak92501/status/1311832183078879232