I guess it's only illegal IN the country. They cannot enforce that outside of their legislation. That means nobody can stop people using imagery to contribute to OSM. But if somebody has done this, try avoiding traveling to it.
Chongqing looks fun. Not only modern cities multi-level - Edinburgh old town also fun, old stone castle-like buildings, ±12 floors one side for 4 on the other, as it straddles an old volcano (does lack north-south transit).