Coyle and Aleta are different, however, in that Coyle is travelling and absorbing power (hence all of the different versions) while Aleta is split and has a different version existing in each plane (Talich, Old World, Avarrach, etc).
The Overseers of Solace are from, predictably, Solace (as opposed to the demons who are from Torment) which is not a plane like the others. I use a fishstick sandwich analogy to describe IW's multiverse, and in that analogy Solace is the top bun, not one of the fish sticks.
So... as the lore stands, there's no reason for there to be an Overseers Aleta. And there's little reason for one of the other Aletas to join them.
Of course, LM may make one anyway and rewrite the lore to their fancy, as is their prerogative.