Hello Jim,
You might find the following post useful regarding different NDMP backup options:
FAS2220+ Entry Level FAS backup to Tape - Connectivity options (SAS and NDMP) (https://communities.netapp.com/thread/25746)
I hope this is of some use.
Adrian
p.s. CIFS/NFS is file level, iSCSI/FC is block level, the flexvolumes have different properties set for very different reasons. NetApp has great features for providing more efficiency backups using the snapshots & snapvault for D2D backups and then it will allow you to backup to tape more effectively so you don't have to backup to tape in-efficiently on a daily base.