Yes, it's very easy to replace the Login with Facebook button that's part of JomSocial, and we're planning to have automatic integration over the next few months.
For now though, please see our
JFBConnect integration guide for JomSocial
, which shows the minor edit to the JomSocial template file you'll need to make.
Hope that helps, but if you have any other questions, just let us know.
Thanks,
Alex