We don't currently have an Open Graph plugin for JComments. There's quite a few plugins we have on our to-do list, and JComments is one. However, I don't have a timeline on when it would be completed.
The Open Graph plugins themselves are pretty easy to make. It's about 50 lines of code to setup and detect JComments pages. To create it, we really need to understand their extension, which is the most difficult part. If you're interested in contacted the JComments developers for such integration, they're free to contact us, which speeds things up quite a bit if we can cooperate.
Thanks,
Alex