The vmware probe Auto Monitors on a VM power state do not alarm when the VM is powered off. This behavior was instituted based on repeated customer input. Consensus opinion was to generate no alarms when an Auto Monitored VM was powered down.
The workaround for this is to set a Static Monitor against the Power State of important VM's.
Set the Static Monitor to alarm on !=1.
The Static monitor will always check each cycle, and the power state will switch to something "not 1".
Please also note that Static Monitors have their drawbacks. In vmware version 5.x, Statics deployed against resource elements that do not exist are alarmed on their 'non-existence.' They should only be deployed against VMs that are more or less permanent. Static monitors against temporary VM's that may be powered down or decommissioned should be avoided.