OBR has allies in the story of Wrath of the Everchosen
-Only a minor spoiler for WotE ahead, nothing about the conclusion. People who comment please avoid spoilers as well-
So in the story of the book, one of the first things Katakros does in his plan to seize the Eightpoints is realize his units will hard pressed to push through the defenses of Chaos’ Dreadholds. In a move a smart general would make, he sends word to Lady Olynder to lead her procession as a vanguard for his forces as they can pass through the walls and gates with ease, and open the way for his soldiers. In the first battle, the death alliance even raises the bodies of the dead chaos defenders as zombies as send them through the Endgate as chaff to cover the OBR advance.
This happens several times, showing narratively, that Katakros is not above using other types of undead when he rightly realizes that they would be better tools for the job than his elite troops. He willingly initiates alliances with Nighthaunt and Deathmages (who made zombies for him). Let OBR use, and be, allies on the tabletop. It would only take one sentence to solve the “relentless discipline for command abilities” problem, by not letting RDP be used for command abilities of non OBR units.
It remains one of the more disappointing choices in my eyes that Nagash’s view of a united undead-topia are spearheaded by a force unable to take or be allied in other forces, solely because of poor design choices.