"will the Chinese Firewall interfere with any web development activity they have to do" - Most of the Chinese programmers know how to bypass the firewall by using VPN or shadowsocks.
Rails developer here, I have been following remote job listing sites for a really long time. Its frustrating when most of them set limitation as for "US"/"EU"/"NA" citizens only.
I have met several Chinese programmers through out the years and was always impressed with their skills and work ethics.
They have several websites blocked like Google, Facebook (no OAuth integrations). Anything that involves networking might suffer. They would probably get a police visit if the firewall has triggers for sshing into a server (common in devops). Not joking: https://github.com/ukanth/afwall/issues/420#issuecomment-262...
Maybe they could work but would have serious limitations I guess. In a "communist" country, don't even know if they have a tax status for freelancing given the government behaviour.
The only work around would be to have a based company in China to outsource.
Things like Apple saving data of mainland China Apple IDs in GZData concerned a lot of people.
[EDIT: Typo fix]