It's not consistent, I've seen the monsters go after non-pioneer stacks and occasionally other AI, but often they just get ignored and they suicide on my units instead.
I think there is an obvious difference in valuing between at least certain AI units and the human units, that isn't based on any status I can tell.
It's possible I could be wrong, but it doesn't seem that way right now. It's also possible this is situational.
At the very least, the AI does need to build fewer pioneers, it's ridiculous how many I kill when I'm at war.
