I am sure every shot is different, especially around greens where the approach might be a 2 iron or a 9 iron, with the lofted irons typically stopping quicker.
It only takes a few inches of lip above a bunker to keep all but Katrina sized rainstorms out of a bunker. I would actually think that mowing the collar all the way to the bunker lip would have a greater effect on directing balls into bunker than rough and could be used, if mowing right up to the bunker edge isn't a problem.
Depending on height of cut, balls tend to keep rolling at anywhere from 5-10% so you could slope a green down to a bunker, and then provided a 2-3" deep swale, and perhaps a ball hit hot enough would roll down the slope and hop the little swale, if that is what you were looking for.