Please find the answer below:
1. GUI - Under Manage Nodes -> Group by : SNMP Version -> you would see labels listed with 0,1,2,3. Click on 0 its as good as non SNMP Servers.
2. If you want to go with Report Writer -> Create a Inventory Report -> Under Filter Results create a filter -> Object Type is not equal to SNMP (You would find this under Network Nodes -> Node Details -> Object Type)