Right, just checked again. Apart from the listed unique spawns, only Vanskerry Sea Raider Army, Peasant Revolt Army and Azi Dahaka Death Cult Marauders are affacted.
The existance of another spawn rate modifier is uncertain. If there isn't, it needs to be created. Either way, it is rather time-consuming to find or do something manually. I can't promise anything, I have tons of things to worry about/focus on. But I added a reminder for myself.