We license per socket so the amount of vcentre environments isn't important for us. If I understand your question, you are going to work with a Robo scenario. In v9 we already made lots of enhancements to those scenario's so you can have a repository per remote site and let the backup and / or replication of those VMs land locally (local repository) in that remote site. Ideally, considering the 3-2-1 rule, you might even consider doing a backup copy job after that (like once a day, when the WAN connection is not used (after office hours) to one of the main sites so you have a secondary copy at your main sites also.
So as long as you have your sockets licensed you are good, and you can design your Robo offices with local backups to a local repository (which could be VMs and without the need of having an additional B&R server) or you can even install different B&R servers (one per location) but do know that you then might need to contact your sales rep to get licenses split. But I think the preferred method would be the first
Hope it helps