You use the word 'help' in a very broad sense. I would ask, help with what? I think you would have a hard time finding someone who thinks that physicians (most of whom are non addicts/alcoholics) are not useful in assisting people with detox.
That is to say, there are many forms of "help". One of those is emotional support. An essential part of that support is often empathy. People who have never had a substance/alcohol problem cannot relate as effectively to someone recovering as can other drug addicts or alcoholics (as the case may be). They cannot quite put themselves in the shoes of those who are currently struggling. Can they provide support? Sure. Is it always as effective? No, not by a long shot. In some respects it takes one to know one.
There is a big difference between support and expertise. It's best to get both, and if all those qualities are characteristic of the person who is helping, so much the better.