Monitor that the newest backup is less than N hours old.
I have cron on all of my systems email STDERR to me, STDOUT is redirected to the normal logs.
One you clean up your crons, you really only get email once a month or so when something breaks.
0 1 * * * backup >/var/log/foo 2>&1
I do this 0 1 * * * backup >/var/log/foo
My errors are emailed to me via standard cron conventions. Normal logging is available for me if I care to look at it.