Hi,
I've never seen any reference suggesting NDMP may work with directly attached SAS tape.
What I normally suggest, is to attach a library to a media/backup server - you can still use NDMP, but the data will go via LAN to a media server, and then to tape (it is still host-free method though). Many NDMP-enabled backup application can use it, e.g. newer versions of Backup Exec.
Regards,
Radek