With vSphere Replication, a minimum of one/maximum of 10 vSphere Replication appliances are deployed at each site regardless of the number of hosts. The amount of vSphere Replication appliances depends on the number of VMs to be replicated (200 VMs per replication appliance).
vSphere Replication virtual appliances are required at the source and target sites. Required number of appliances depend on the amount of virtual machines to be replicated.
VMware, vSphere Replication/v8.1, bundled with vSphere