Do meant by orphan hubs those at where indexing groups is done. That is at the Account Page link to Groups. In that case an orphan hub is merely one that is not in a specific group or in other words the Hubber has left it pending. If meant are Hubs that have been unpuplished by the Hubber, then yes they can be activated again by republishing. But, they will go through the QAP process again to receive or not a Feature status.