dump to remote tape is using rmt protocol that is based on rsh authentication. So you need to add source filer to /etc/hosts.equiv on destination.
But that is not how NDMP will work. In case of NDMP you can either backup to locally attached device (tape) or initiate remote backup to another NDMP enabled host. No rsh and/or rmt is used in this case.
I do not really understand the second question, but I assume you need to add second controller as BE client. Or add (another) tape drive to second controller. Do not zone the same tape to both controllers unless BE supports drive sharing. Usually it is separately licensed option.
The reason of my question was that NetApp hand written commands doesn't support three-way-backup but RMT protocol of which you spoke.
So, three-way-backup type will be used by BackupExec for backuping data up from the NDMP enabled host that doesn't owe tape drive (in my case second controller in FAS2020) to another NDMP enabled host with locally attached (zoned, by fc switch) tape drive.