vCenter Heartbeat uses an "Active-Passive" architecture so essentially you have one active vCenter and a passive vCenter which will take over the services if the active goes down. The main purpose of Heartbeat is continous availability, not load balancing.
Linked mode is neither a load balancing solution. It just provides you a "single pane of glass" for management of multiple vCenter servers.
I understand that, but I'm thinking that can each vCenter at each site be load-balanced? It's just s hypothetical question really, the customer may ask and I want an answer I can give them. It's probably total overkill anyway and I don't think Heartbeat is the answer due to the type of system I'm trying to protect.