So I made a custom sovereign with the Umber faction. I know they are not getting any love and have basically been dropped off the list for faction changes, but I liked them and seeing they were still there made a game with them. After a bit of playing I managed to capture a location that puts out snakes, the large magic resistant ones (the name escapes me for now). This is when I got a taste of the changes to monster lairs and allied monster units. Within no time to my surprise the lairs started pooping out high quality no upkeep snakes! I'm halfway through the game right now and have yet to use a regular army. A combination of Bears (I picked beastmaster as a profession) and snakes have basically been the armies for my heroes. Even quests that generate the snake lairs for a different purpose: drop an outpost, more free snakes. Hell I killed Torax with snakes and magic.
As the only faction with the trait that allows them to pickup najas and other snakes, with beastmaster the faction is oddly enough different enough with almost no effort from the developers to make a very different playing experience. The reason for this though is the lair mechanic where the lair just spits out monsters till it hits a certain preset limit. This is very different from the method (a patch or 2 ago) where taking darkling etc lairs allowed to to buy them like regular units. The question underneath is are these changes intentional or is this something accidentally lining up since it was a faction that was dropped from being a developer focus? There are other creatures in the game that have the lair mechanic (mercenaries ogres, darklings) but none so far IMO seem to gain the crazy benefit the umber do with their no tech required monster friend race trait. Add the techs that allow you to get other lair units you have a rent-free army (I have diversified into mercs and ogres).
If its not a bug, then hey might as well leave the Umber in. With the change to the lairs you already made them potentially way different in practice than a lot of the other races.