In the case where you have one vCenter and vsphere replication replicating between hosts you always need them in order to do recovery as this is manual step of the process. In the case of replications between hosts in different vCenters you need the target vCenter and its VR appliance to do the recovery. But again - it requires manual intervention for the recovery using the vSphee Web Client. In case you are searching for orchestrated process you will need Site recovery manager, which however won't work in the case of one single vCenter scenario.