Jason,
We have not included this type of functionality in the product yet: to suppress the message when the admin wants to...this would be a good scenario for that ability.
As you mentioned, the NDMP agent is out there, but that requires a device on that filer to backup to, so I don't know if that would fit your environment. This would create successful backups.
At this point, I would recommend requesting an enhancement for this ability to suppress the message at http://enhancement.veritas.com. While this has been discussed, the more feedback we get for this, the more weight it carries.
Thanks.