You will not be able to use tar or gnu tar to read
NDMP backups. They are not written using the same
method (i.e. Tar format)as regular NetBackup backups.
They are written using the NDMP dump command which is
an entirely different format. NetBackup when
performing backups or restores relies entirely on the
NDMP server to write or read the data. You must have
an NDMP server at the new location in order to recover
these tapes. It doesn't necessarily have to be a
Celerra but does have to support the same NDMP version
as the Celerra does (which most of them do). 

Jeff Redington

"A wise man once said 'Wherever you go, there you are'"
      -Mike Brady