I have had a similar experience with Bronzong. I wanted to test something like this a while ago for my personal enrichment, and I have come to the rather (in my opinion) unscientific conclusion that the AI does, in fact, know your pokemon's ability, but not its item.
I also did a different, but I think, complimentary, test to the observations that Jumpman stated:
I used to use a Tyranitar (with boltbeam), sceptile (choicescarf), and DD Dragonite team in the battle tower.
Tyranitar initially had a focus sash, but then I put that on Dragonite. My reasoning behind this was because Dragonite had DD and Outrage, and did a lot more damage subsequently, but would frequently get one hitted. I also noticed I was losing to a lot of typhlosions with focus blast (out of 35 recorded uses in four days, the AI missed 1 time). So I placed a chople berry on Tyranitar.
I do not know the full set on Typhlosion, but I am almost certain that it had a more damaging move than focus blast (factoring in sandstorm) and the AI always chose to use focus blast even though after the chople berry it did less than 50% damage (somewhere between 40-49% iirc [I havent used this set in 6 months, minimum), and I know that I took more from a STABed overheat or fire blast.
I don't know what conclusions you want to draw from this, but I think that it tends to corroborate the already articulated point, particularly the feeligns espoused by our colleague, TRE, who I consider a very learned source on the battletower (sorry if that sounded sycophantic).
Also, an event that I encounter frequently:
I use choice specs gengar (a lot) in the battletower. After battle 21 I face a very high number of torterra for some reason (this is a consistent occurence). Even though I am certain that torterra could kill my gengar (who has a paltry 123 HP at lvl 50 XD) with either wood hammer or some some other attack, the torterra always tries to neutralize my levitate with worry seed. This turns what would be an almost certain death for the little imp into a free kill every time without fail (I can't provide exact damage calculations, but typically with ~244 spAtk after cspecs it does between 94-100% damage so sometimes [1 out of every 4or5] I'll OHKO the torterra).
I don't know how much my schtick adds to to the topic at hand, but I hope I can expound upon some of the points already articulated.