I'm not sure about the CLI commands, but there is a Tunnel alarm OID apTunnelAlarm=1.3.6.1.4.1.4329.15.3.19.4
You can also probably create an alarm in netsight based on RU session manager syslog events, if you just want to see when a backup tunnel is activated e.g.
"RU Session Manager Wireless AP activated backup tunnel"