Yes but it's very very slow (as in on the order of minutes for a page to load). I think this has to do with how Stack Overflow's front-end code is written. There's some non-essential Javascript that is blocked by the Great Firewall which blocks the rest of the page from loading for a long time before the page gives up and displays a banner that some Javascript failed to load.

All programmers I know have software to circumvent the Great Firewall and view it as a necessary condition of their profession.

Yes.

Many Chinese developers are not fluent English users though. There's a "Chinese StackOverflow" called segmentfault.com, and I often see people asking fellow developers in WeChat groups.

Source: Am Chinese in China