All the traffic would be tunneled, so unless they're using heuristics or ML to determine "phoney" and "desktop/laptopy" timing in the packets, they can't really tell what's going on.

Just about entirely. They could block the VPN or try to say that it's got to be teathered but it's much more difficult for them to say that or back without causing serious issues for customers.

Who knows? It’s still obvious if you look at the traffic patterns, a VPN can’t hide that. But as long as you stay under the radar they might never know. Or you might be booted and blacklisted from the network.