There is absolutely no reason why addicts shouldn’t attend AA meetings. However, AA has traditions that are important to the fellowship and to many of the members. One of those is that they generally confine their discussions to alcoholism and recovery from alcoholism.
Disregarding the fact that alcoholism is an addiction like any other, and disregarding the “a drug is a drug is a drug” of NA, keeping drugs out of the conversation is the custom at the majority of AA meetings. Everyone attending — cross-addicted people like me, and people not addicted to alcohol at all — should follow that custom in most cases. It’s simply good manners.
There are, however, situations where a person is in crisis, and simply needs a meeting of whatever kind. In that case it is perfectly proper — hell, it’s a life-threatening emergency — to say whatever we need to say in order to get whatever kind of support we need. What I would do in that situation is simple. I’d raise my hand and say “I’m not an alcoholic, but I really, really need help because I’m about to use. Will someone come outside and talk to me about it?” I would probably be invited to stay and say what I need to say, and if not I’d have a horde of people headed for the door with me.
Really, the substance has nothing to do with it. What matters are the emotions, the behaviors and the solutions. Those are the same for all addictions, and anyone should be able to talk about them in any meeting without ever mentioning alcohol or any other drug.