I've always considered devilites to be intelligent. I mean, how do you run a giant, multi-city-wide corporation if you can't read, write, think, communicate, and plan?
But seriously, about lore. At this point there are two possibilities as to what's going on.
Possibility 1: OOO has an incredibly complex lore web that they are revealing to us very cryptically and slowly.
Possibility 2: they don't have anything and they're making it up as they go.
I'm pretty sure fiends are ranked as intelligent life. You see pit bosses speak, for one thing. Plus, there's Sullivan, the trinket guy. He's a fiend and you can talk to him.
Another is that compounds were described as containing a family of minis controlled by an intelligent force. The minis are beasts, undead and slimes while the other families capable of appearing in compounds are gremlins, constructs and fiends. I believe the idea is that those three families are sapient, whereas the families with minis (or at least just the minis themselves) are merely sentient.
"The Compounds feature the remains of some sort of unknown facility, where more intelligent monsters await, harvesting resources or perhaps attempting to power up the derelict machinery."
This says nothing about the intelligent life containing the minis, just that they wait inside the compounds while the minis roam around outside.
I've met that room several times -> love seeking out the harder clockworks levels.
The other things that spawn there are:
Cash
a few silkwigs
a few pit bosses
Dunno if that would give you more insight :p