A fabric zone is required for the drives to be seen by the client with the
Storage Agent just like the TSM Server.  You still have to define the pseudo
library and drives to allow the Storage Agent to see the drives.  What the
Drive Mapping does is maps the drives in the TSM server to the drives in the
Storage Agent client in a platform independent way making it possible for
the drives to be shared.  The control point is the TSM Server for the
allocation of the drives and the mounting of the tapes.

Review the Atape driver for LTO.  I believe that it supports alternate
pathing but do not remember. That would be the reason to zone both HBAs to
the driver so that if one pathway failed the other could be used.  But, you
still only define one drive to TSM, the primary from the OS point of view.
The Atape driver will failover automatically to the alternate path.

Same for the ESS disk.  You should be running the SDD and dual pathing just
in case the pathway fails.  SDD also gives you load balancing.