@Jace -
I believe I saw a screenshot that showed BackUpBuddy requiring a user to enter the domain that the software was being used on. I would assume that is to “phone home” and check that the license covers operation for said domain in order to function. Does the software do this? If yes, doesn’t that prevent me from redistributing the plugin as I see fit, as required by the GPL?
Fair questions. I've never tried installing my copy of BackupBuddy on more than two sites, so I honestly can't answer your question. I don't know what would happen if it were attempted to be used on a third site.

If it fails to function as intended, then yes: I'd say that their implementation violates the GPL. I'll give it a try on a separate web site, and let you know.