You can select SNMP on a device's Services dialog box (Properties > Services) and monitor it just as you can monitor any TCP service. This checks to see if the SNMP service is running on the device.
First, you need to add an SNMP Active Monitor to the device.
To assign an SNMP Active Monitor to a device:
Note: An SNMP-manageable device is identified on the map by a star in the upper-right corner of the device.