No tipping in China, if ever there is a need there will be a service charge included/added to the bill in which you have no say.

Also the standard procedure as mentioned above is buying the driver lunch, normally we've had him eat with us as most places at the Great Wall or other out-of-town tourist spots are pretty casual.

In the case of dinner, if it is a driver who is hired for the day, then they normally wait outside in the car. If it is a driver who is going to be working long term for you or your company (depending on specific company policy) we normally give them their own table at the restaurant and they eat and wait there until dinner is finished for everyone else.

The inviting the driver to meals thing is less common nowadays though as some car services have started to prohibit their drivers from joining their customers in this manner. Some drivers will just tell you not to worry about them and they'll hang out around the car until your done.