bkg
Explorer
I've never seen crumple zones built into an ARB. ARB advertises they analyze the OEM airbag and crash absorption systems for each vehicle to maintain the OEM performance and function. I believe this includes crumple zones behind the bumper, not the bumper itself. If the bumper itself were to crumple, it kind of negates the value of adding it in the first place.
The newer ARB's are a multi piece design - bumper and mounting brackets. The mounting brackets have the "crumple zone," as I'm calling it, which i'm sure is for airbag compatibility. Older, one piece bumpers for pre-airbag trucks didn't have them (at least the three ARB's I owned previously didn't).