From what i've seen so far, the AI can still be tricked.
Case example, a large rectangular building.
Entrance is on the northern side. Player lets some mercs run along and throw rocks against the western and eastern walls. This will distract enemies inside the building in the vicinity of these walls = looking at the wall.

The player, sitting outside in the dark, stealthily (is this possible or will the door make a noise even in stealth mode ? ) opens the door into a lit room: a) player is blinded due to the bright light suddenly hitting his eyes b ) enemy inside is still staring at the snail snailing along the wall, because s/he didn't notice the door was opened. Who interrupts first ?
I haven't had these situations with my recent play yet, so i don't know how it is solved ingame ; but generally speaking, both sides of the discussion can bring up valid arguments.