Service Monitor or Log file monitor can do this
The most straightfoward method is to use the SiteScope Service monitor to monitor that the Scheduler service is up and running properly.
As for monitoring specific tasks, unfortunately, unless the task spawns other identifiable processes, this is not possible with the Service or Process monitor. However, it is possible to instead use a Log File Monitor to monitor the Task Scheduler log file at C:\WINNT\SchedLgU.txt. It contains entries like the following after a successful dispatched task:
Finished 1/17/2005 1:58:10 PM
Result: The task completed with an exit code of (0).
The Log File Monitor could then content match for the exit code (0 being good) with a regular expression in the Match Content field. Then the error condition could be set to error if the status is != 0.