Putting run_probes in cron is a reasonable first-cut, but as it gets
longer, it doesn't work out. Strictly speaking, cron is the wrong
model; don't want to say "run every N minutes", do want to say "delay
between runs". Might possibly want to say "maximum time to run" but
that could be done directly in the tool. The concern is noticing if
it ever stops running and restarting it.
This comes up enough that it surprises me that it isn't part of a standard tool - but that's true of lots of things lately. (Rather, keeping something running is the traditional job of init - but there isn't really a good user-level configuration for it.) Further digging turns up daemontools, which is unlicensable, and runit, which seems to focussed on serving as the primary init.]
So, nagaina now includes run_forever, and an @reboot crontab entry.