By default, a file system usually needs to be backed up.  You may have bad backups if it happens to contain something like an Oracle database, and you won't have an application-consistent backup, but at least you'll have something. 

It definitely gets harder with active/passive clusters since NetBackup doesn't really support them very well, but something is better than nothing.  When your admins tell you how the file system really needs to be handled, you can adjust your backup policies to do the right thing.  By if they forget to tell you anything at all, at worst case you'll have a generic file system backup.

We tend to do most of our backups with a generic all_local_drives type of policy coupled with some exclude for things like database volumes, and then use application-specific policies to cover them.

Simple is always good.  The less you have to muck with it, the more likely you are to be successful.