1. There should be absolutely no problem with Epirb rental/hire (or borrow?) etc as the primary contact details (1 of 3) especially in a hire/rental situation should not be dependent on vessel details
2. AMSA's first move is to call the first point of contact and this is where all the verification should be done. This is the whole point of registration.
3. However IF the listed contacts (ALL 3 plus 2 points of contact each) are not available then you have some very real (and legal) issues and this will be where the "owner" of the Epirb has to make sure ownership requirements are 100% totally covered