Retail FX trading is neither illegal nor made difficult in China. Most of the larger retail FX brokers have representation and facilities in mainland China. Your tax situation will be determined by your nationailty and domiciled status there, just the same as anywhere else.
Most brokers offering FX retail trading facilities will operate under SIngaporean fiscal regulatory rules.
If you're going out on a corporate basis I imagine you'll be in a major hub where infrastucture and facilities will be good. As is the food...
In the unlikely event you're being sent 'up country' then not being ablse to trade will be the least of your worries.
Thank you very much for that info. You've put my mind at ease.