In Coop you can sometimes see bots' gun poking through walls. This gives an indication on where the bots are.

I expected that weapon collision detection would also apply to bots, and would be rendered in game.

Yes you are right. Happens very often.
Their weapons barrels shows us their position outside the building when they are very close to the doors or walls.

With a 5,56 mm or 7,62 mm caliber rifle you can easily shoot them through doors and walls in such cases.
Too easy if you ask me