I worked on this similar kind of the solution in my previous company who has mid range of customers having not more than 30 to 50 VM's. But we never replicated their VM's to our company datacenter instead we used to replicate their VM's to their branch offices over 10 Mbps Leased Line (LAN to LAN VPN). Here is that soultion
1) 4 ESXi hosts and HP SAN in Head Office, loaded with vSphere 5.1. This setup is running with One vSphere Replication Instance and 10 VM's--> Head Office
2) 4 ESXi hosts and HP SAN in Branch office, loaded with vSphere 5.1. This setup is running with One vSphere Replication Instance and one vCenter Server having 12 VM's --> Branch office
3) 10 VM's are being replicated to Branch office and 12 VM's are being replicated from Branch office to Head office.
Here only challenge I have seen is network designing. We have to make sure IP addresses should be same as customer network.
Note: You can't replicate VM's to Storage directly using vSphere 5.1 (not sure about 5.5). For this fulfillment,you need SRM for Storage Level Replication
Hope this information may helpful.