OpManager helps you monitor the performance metrics of any device that supports SNMP. The monitors for CPU, Memory, and Disk Utilization are automatically associated for the SNMP devices based on the device template definitions.
For example, consider you've associated SNMP-based monitors to the default template for a server type (say Linux) in OpManager. So from then on, all Linux servers discovered into OpManager will have those SNMP-based resource monitors associated by default. This doesn't apply only for just one device category, but these definitions can be used to associate related monitors to any SNMP-enabled device.
If you do not see these monitors associated to the devices, it could be due to any or all of the following reasons:
It is recommended to use WMI or CLI to monitor Windows or Linux devices respectively. But if both these protocols aren't available or if you want to monitor additional metrics using SNMP, you can also do that in OpManager.