SRM is deployed as a Windows application. Nearly all deployments run in a single Windows VM at each site. For vSphere Replication some extra VMs are required.
VMware SRM is required for each site, running on a dedicated server/VM or installed on the vCenter Server for smaller deployments. Each sites requires its own vCenter Server.
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).
VMware, vCenter Site Recovery Manager/v8.1, w/ vSphere Replication