In order to restore the vCenter Server you will need to add one of individual ESX(i) hosts to Veeam Backup & Replication. This will allow you to target that host directly to restore the vCenter VM.
When adding the standalone ESXi host to Veeam Backup & Replication if you receive the error:
VMware ESXi with name '<hostnme/fqdn/ip>' already exists.
Please try using an alternative way to contact the server. For example, if you tried adding the ESXi host by its IP address, instead try using it's hostname or FQDN. If you tried using the hostname\FQDN, instead try adding the ESXi host by its IP.
Information regarding the IP and Hostname of a standalone ESXi 6.0 or newwer server can be found:
Information regarding the IP and Hostname of a standalone ESXi 5.5 or older server can be found here: