I Would like to share a tech note usefull to understand NDMP backup with Netbackup, hope this could help you as well.
About remote NDMP and disk devices
This remote NDMP feature involves backing up NAS data (Network Attached Storage) to a storage device that is configured on a NetBackup media server. NetBackup supports disk devices on the media server.
Here is the link,
How to configure NDMP backup, can be found in below link