Do Mechanics need to be Ase Certified – No
First thing first, ASE (Automotive Service Excellence) Certifications are optional and I do personally believe they should stay optional. Good mechanics shouldn't be limited to how many certifications they obtain. There are many good mechanics out there that doesn't need to look good on paper, they let their work show it for them. Many people have grown up working on or around engines and they've become great at what they do. No real reason to pass up a great mechanic for a mediocre mechanic who has an ASE Certificate.
ASE Certified Mechanics are usually found in top of the line auto or truck shops. To some extent there could be places where employers need to make sure their mechanics know fully of what they are doing, so knowing they are certified in certain areas would be plenty helpful, but none the less, a mechanic's abilities shouldn't be limited to whether or not he has an ASE Certificate. There is a good reason why mechanics generally do not need to be licensed to work on any kind of road vehicles on account of anyone with a decent amount of automotive electrical or mechanical knowledge and can turn a wrench, can do some vehicle repair with ease.
For the most part people may only rely on ASE to tell them whether or not if that mechanic can fix their vehicle. But what does not come up is whether your getting charged a reasonable price. There could be many ASE certified mechanics that charge an outrageous price just because they are certified. While you could go over to a regular mechanic and he would get the job done exactly the same but wouldn't charge a ridiculous for parts and labor as the ASE Certified mechanic would. An ASE mechanic would be more likely to use an sponsored high dollar part for your replacement or repair, whist a regular mechanic would use parts that he knows that are reliable from experience and that is at a fair price.
I would say an ASE Certified Mechanic would be a good idea for employers of a top of the line auto shops or in auto factories, but I feel for the most part, ASE certifications isn't necessary for all mechanics. If you know a mechanic personally or from a friend, and they make their own repairs, then that should be enough for a good mechanic.
