waiting for some info...
Adding a vCenter for monitoring will also automatically add all of the vCenter's child ESX hosts for monitoring in VMAN as nodes. VMAN will be able to monitor objects and metrics that match the permission level of your credential.
https://documentation.solarwinds.com/en/Success_Center/VMAN/Content/VMAN-Add-a-host-for-monitoring.htm
If you are adding a virtual object, it will send you to "Add A Virtual Object For Monitoring" page.
You use Network Sonar Discovery If you are planning to add those hosts as nodes (ICMP or SNMP).