Most dyed-in-the-wool four wheelers know that ASE certification means little or nothing; and individual's experience, knowledge and reputation mean everything. The seasoned four wheeler knows several knowledgeable mechanics at several shops who they go to for help, it's a trust thing! ASE certification apparently is easy to acquire ... there are too many certified punks in 4x4 repair shops today that can't read a repair manual to resolve a 4x4 rig problem,and commonly recite myths and bias about which vehicles are best, and the best way to setup an offroad 4x4 rig! From my experience evaluating shops, most dealer ASE certified mechanics ( who are promoted as being superior mechanics by vehicle manufacturers) know little about lockers, trannys, and t-cases, let alone axles.
My experience with mechanics is that ASE certifications mean some things. At minimum it means the person has shown enough knowledge of the underlying basic mechanical theories to earn a passing grade for each area in which the mechanic holds a certification. I know to many "experienced" mechanics that rely almost entirely on diagnostic trouble codes, shotgunning, TSBS and tech lines to diagnose problems. I.e., the no code = no problem crowd. Anything that the "tools" can't diagnose and they are lost because they have no knowledge of the underlying theories. ASE certs also means the mechanic has shown they can read, apply what they have read and have shown the effort to at least try and educate themselves on the basics.
Saying that, Jeeps are different from the average grocery getter- a mechanic's experience with other vehicles may generally cross over, but like most other professions, experience matters most. Its the age old difference between understanding, knowledge and wisdom. ASE certifications means (presumptively) a fundamental knowledge of the underlying basic mechanical theories. Understanding is different from knowledge in that understanding usually comes from experience. Wisdom comes from (hopefully) learning from the mistakes made while obtaining the understanding that the knowledge could have made less painful.