I have indeed attended a couple of those meetings (I like the coffee). I have yet to hear the words "I need to vape or I am going to do something else". If I did, I believe that person would need a lot more than a meeting.
When they banned smoking people didn't stop seeking help from these groups and not allowing vaping isn't going to stop people either. Allowing it may however turn some people off who are offended by it (rightfully or not). There are a lot more people who Don't vape than those who do and they should not be made to feel uncomfortable.
As you say, each group makes it's own rule and some times the rules are set by the owners of the meeting place. But, I would caution you on thinking that those who don't wish to see vaping in a meeting are all resentment fostering anti-vapors. Some of the people responsible for these rules being made just want to see the subject of the meeting remain the focus. Some of these people may not even be anti-vapors. Some of them may even be vapors themselves. Heck, some of them may even post on this web site, in this very topic, right now.