Hi tojo45.
I fear you may have issues getting a response on this one as
not many RH users use source control and of those that do most use
other SS tools. However, I would agree that in theory you should be
OK as all the source control s/w will do is check in/out files. It
shouldn't care about what files they are. Also as RH6 and RHX5 are
largely the same you would have less risk than if you had RH7
licences.
I'd create some backups of RHX5 and RH6 files and run a few
tests. That will probably be the only sure test.