I can't speak to the "crumple zones" in an ARB bumper but your (front) air bags are triggered by an independent sensor that activates the airbag ignitor if the rate of deceleration of the vehicle exceeds a certain thresh hold. Bumper shouldn't have anything to do with it.
Crumple zones are more about absorbing and dissipating the energy of an impact so it doesn't get transferred to the driver or occupants.