Hi,
You can have at most one vSphere Replication Management Server (VRMS) per one vCenter Server and the limit of 500 incoming+outgoing replications is per VRMS.
If using VR together with SRM, you can deploy additional VR-server-only appliances (w/o VRMS in them) for better routing of replication traffic to the target datastores (better locality of VR server to hosts that have access to the target datastores).
Regards,
Martin