Hey,
Any automated monitoring job is based on the assumption that the tool automating it will work fine. With this assumption in mind, option 1 seems like the simplest and most efficient way.
Of course, yet another precaution you can take is to schedule email to DBA if there is any error in the backup creation script itself (mail if there is anything in the stderr), which will also take into account any error generated by pg_dump/dumpall commands.