LTM's external monitors are incredibly flexible, fairly easy to implement, and especially useful for monitoring applications for which there is no built-in monitor template. They give you the ability...
FYI: When the external monitor script outputs "UP" than the deletion of the PIDFILE never occurs, neither does any further commands after the output of "UP"
It does however delete the PID if the monitor fails. I can only assume the F5 kills the script immediately once any output is detected...