You can do the usual stuff like monitoring disk usage, running processes, etc.
Some fancier things like monitoring drives or the scratch pool can be found via google. Since NetBackup is higly scriptable, you can write your own monitoring scripts to check what you want to check.
You could also create passive checks using the scripts called by netbackup after specific operations. e.g. you can report the status of the last backup by integrating the nsca in your /usr/openv/netbackup/bin/backup_exit_notify script.
