It doesn't have to be a professional or a certified person, but my argument for a professional is that they are more equipped to handle difficult situations that might come up during a session or when their clients give them very difficult problems to work with.
One example why I think someone a professional background is better- There's this reply I saw on Asperger Experts Facebook page. (Don't get me wrong, they are great at what they do.) However, because they don't have the education and/or training like I do as a health professional, I see that they made a poor quality reply on their fan page to someone who asked them a question. The question was about a parent asking what their advices were for her child who are pretty poor at ball sports and she wanted to know what sports would be good for her child. They said that practice can make better. To a certain extent, this is true. However, this is NOT the best answer because they have failed to discuss about possible factors why her child might be struggling with ball sports- which I later added about gross and visual motor skills and told the parent to try to see if there were previous gross and visual motor evaluations done on her child and if not... then she has to be a keen observer of what is really going on with her child whenever he engaged such ball sports to see if there are particular areas of deficits in common.
So, I would say if an autism life coach has a solid professional background (not just with their personal experiences as autistic individuals or caregivers) are safer bets.