Hello again,
I would recommend to use WBRM instead of the SNMP agents and snmp default stack in Windows servers.
For linux servers you can only use snmp agent and thus snmp.
For esx you can only use wbem for 5.1 and above. If your server is a gen 8 or newer you only use the Agentless Management Service. This is the latest and greatest way of monitoring your hardware.
To start i would use Windows or unix credentials to create a trust between SIM and the server you wa t to monitor.
this csn be done with a repair from configure > repair? If you set the wbem agent install on in the first screen, the second . screen wbem settings and a trust. If needed you can also set a non admin account to be used later for discovery.
The account that runs the repair can be your own account, for discovery you should create a service account with either admin rights or a account that you gave with the repair option to discover with a non admin account.
This should be enough for now, lets first try to identify your servers with the options discribed above.
if you get this running let me know or if you run into problems. If you have problems please include a discovery log for a failed server to troubleshoot.