Unknown type for discovered VMs

Hi - when I add a vCenter virtual appliance to perform an automated VM monitoring, the VMs are correctly added to OpManager - but the discovered VMs are of type "Unknown". I have created a set of templates that via SNMP that correctly recognize each host (tested with the VMs IPs) and monitor a different subset of metrics, but I can't find a way to automatically associate the SNMP credentials to the automatically discovered VMs.
The only workaround I found so far is manually re-discover the VMs adding the SNMP credentials, but given the number of servers I have to add (a few hundreds) this is not viable.
Please advise me on how to perform the vCenter discover and the subsequent SNMP discover automatically (the vCenter discovery alone is not enough).
Thanks,

Marco