The specific TN is probably no longer available because NBU 7.6 is no longer supported.
Please upgrade NBU to supported 7.7 or 8.x version before you even think about NBAC configuration.
Even with available documentation, NBAC config is not easy. My previous attempts resulted in Support calls.
You can only log Support calls for supported NBU versions.
Version 8 manual: NetBackup Security and Encryption Guide
Assuming I have updated to a supported level, are there any gotchas regarding linking AD to NBU on Linux?
In NBU 8.2 NBAC will be replaced with RBAC
NBAC is a beast to use and manage due to the way its implemented. RBAC is build from the ground into the product.
My recommendation right now is to wait for 8.2
