As a Chinese developer and user, I cannot visit or use Googe Ajax directly.
The IP addresses that Google Ajax using in Chinese location are
216.58.0.0/16 and
173.194.0.0/16 were blank-routed,which means that Google's IP addresses was blocked.
You asked "it is not possible to access Google Hosted Libraries (like jQuery) from China", I just say "yes".
It it possible that Google can change their DNS records to their servers that using IP addresses in China mainland (
203.208.0.0/19) when requests from China.