vSphere Replication has certain operational limits.

To ensure successful virtual machine replication, you must verify that your virtual infrastructure respects certain limits before you start the replication.

You can only deploy one vSphere Replication appliance on a vCenter Server instance. Deploying more than one vSphere Replication appliance is not prohibited, but might lead to unexpected results.

Each vSphere Replication management server can manage a maximum of 500 replicated virtual machines.

See http://kb.vmware.com/kb/2034768 for more information.