My understanding is that ARB makes some of their bumpers "airbag" compliant by adding crush cans so that the decel curve matches the existing factory, with the result that the bumper pivots much like a brush guard and does huge amounts of damage (saw a pic somewhere where someone was bitching about how their air bag bumper took a moderate collison and bent down). I think air bag crush cans are on jeeps and landrovers (my quess is more lawyers own those).

Airbags can still deploy with bullbars, but I am told that they may deploy sooner all things being equal due to their stiffness. But there are so many variables in an accident I am not inclined to worry about it.