I was excited to see this feature in the release notes for 6.3:
Previously, enabling the SNMP Trap outbound plug-in caused every alert and update to be sent to the destination, which in our environment was thousands a day, most of which we didn't want in our event management tool, so it required a lot of filtering and strain on that end. The documentation for 6.3 still indicates this is the case:
vRealize Operations Manager 6.3 Information Center | SNMP Trap Plug-In
What I found was previously enabling the SNMP Trap outbound plug-in sent all alerts, but wasn't listed under Content -> Notifications. In the new version, a new Notification appeared mapping all alerts to the SNMP Trap outbound plug-in. To limit the number of traps sent I deleted that rule and created a new notification to send SNMP traps only for the particular alert rules I wanted sent. Just a heads up if you were looking for how this worked, the linked documentation should be updated with information about the new functionality.