Right now I run the program with cron and have that send success/failure email, which I could certainly offload to monit via some mechanism (such as log / drop file as you suggest) to allow monit to detect success / failure.
What I am trying to accomplish is not having crontab entries spread across all of my machines. Right now I am able to start/stop programs in monit remotely from a single centralized crontab (hitting remote monit http port via python script) and as the number of machines grows it is nice to have only a single crontab to manage. In addition, I can fire off that remote script at any time via the monit web interface or from m/monit which isn't possible if it is scheduled in cron.
I'd even be open to adding a mode to monit called "batch" (in addition to "active", "passive" and "manual") that would allow a job to be run once when start is clicked.