Your understanding is good. GitHub doesn't support TFVC. Neither you can install TFVC without TFS; it's one of TFS components.
You definitely can use Git for storing .xpo files in the same way as in TFVC, but the integration to IDE is a problem. I believe you would have to rewrite it completely, nevertheless I've never given it much thought.
Maybe if you tell us what problem are you trying to solve by using GitHub, we might give you some suggestions.