We use custom scripts to create quiesced snapshots, rather than snapmanager, and then dump to networker via NDMP.
It's all fairly straight forward. The saveset should reference the latest snapshot: /vol/somevol/.snapshot/dbbackup.new (or whatever your snaps are called).
The filer needs a backup user and password on it. This needs to be filled in in the networker client. The backup command needs to be filled in as something like: nsrndmp_save -P networker_server -M -T dump (with the appropriate networker server substituted). You also need the NDMP box ticked and the appropriate options in application information.
NDMP (dump) will only backup one snapshot. If you specify a snapshot, it backs that snapshot. If you don't specify a snapshot, it creates a snapshot, backs up, deletes the snapshot. To get 20 snapshots to tape, you would need to run 20 backups... not typically needed.. The way to get the entire volume to tape is snapmirror to tape. The restore is only the entire volume though ( no single file) and every sm2t backup is a full.