Just to add my 2ct, NDMP has different use cases. It can be
- using a (NetApp)-filer as a kind of "tape server" - backup software uses tape drives (and maybe even libraries?) connected to the filer as target for external data;
- backing up data from a filer to filer-attached Tape drives - backup software only as control instance, backup server is not in the data path.
- backing up data from a filer to backup server attached tape library and drives (aka. 3-way-NDMP).
One main goodie for NDMP backup is that file system meta data will be backed up so it can be restored as it was. With CIFS or NFS there always seems to be some kind of meta data loss during transit.
Depending on how well NDMP is implemented on the filer and on the side of the backup software, it might even have something similar to "CBT" to enable "forever incremental" in a timely fashion - I don't know how you'll achieve that with direct backup of CIFS or NFS share.
I'm seeing people moving away from NDMP backups because the amount of data stored in a filer (we have a 'small' Isilon cluster with about 150TB and billions of files) makes it unfeasible. We can't possibly meet any sensible RPO or even RTO, because incremental backups take up a lot of time for treewalks (which files have changed), and even though full backup are actually faster, you can only write about 130Mb/s to one LTO5 drive, so it almost always takes too long for a backup to finish.
To paraphrase a famous quote: "NDMP is the worst form of backup, except for all others that have been tried". It would be great to have Veeam support NDMP, because from my experience Veeam works great, which could mean that Veeam's implementation of NDMP also might be great...