Dave, the Chinese job market is pretty difficult to figure out. Maths in local public schools are mostly if not all taught by locals, especially at primary level. If Middle schools hire foreigners to teach Maths they must have reasons to do so and therefore they must provide their local curriculum. If in higher education, they most likely will ask you for some specialty cert if not BA or MBA with a major in Maths. Some international programs may also offer positions for FTs to teach Maths. These programs usually carry their curriculum. I think, you'll have to seach a lot if you want to go for a specialty subject on mainland. By the way, locals here are pretty good in the subject, usually better than many students in English speaking countries. However, once you get to one of the secondary or higher educational programs in Maths, you may have issues with how the local students reason and/or justify their results.
Good luck and
Cheers and beers