Yes, with some minor limitations as it receives much less testing. I was using 10x with The Machinery (RIP) for some time and the developer was super responsive fixing any C-specific issues (and even added some TM specific features when I asked nicely). If more people start using it for C and report any issues found, it should get even better.

I would say it may even be better suited for C to some extent since that is a much simpler language with less chances for the parser to get confused by some obscure corner case. C++ really is the worst case scenario for a parsing engine, so once it works reliably for that, support for other languages should also become much more feasible.

It's hard to imagine a C programmer so professionally ignorant that he's yet to realize C++ is a superset of C.