It varies hugely. There are loads and loads of groups here and all have their own character.
I know that some people have felt unwanted because they arrived at a big busy group and no one noticed they were new; everyone was chatting in little bunches with their friends and didn't go out of their way to welcome the newcomers. For social butterflies this isn't an issue because they walk up to people and introduce themselves but those who are feeling more nervous can struggle.
Being overlooked isn't a problem at smaller groups, but rejection there can be more hurtful if you KNOW you haven't been overlooked. We do have a challenge at some of the small groups I go to, that one or two of the kids who have autism may feel alarmed and threatened by the presence of new people and their response comes across as very unwelcoming. Parents try to explain to the new parents and children (if they aren't too busy trying to calm their worried child) but it is still tricky.
I don't think I've ever seen a newcomer who was trying to make conversation being rebuffed, but we do have very awkward moments if the newcomer is clearly coming from a different place compared with the others in that group. Home educators vary quite a lot! For example, I can remember incidents such as these, when I wanted the ground to swallow all of us up because we said thoughtless things:
People saying very negative things about teachers, only to discover that the newcomer is a teacher
People making it clear that certain behaviour is required at the group, only to learn that the newcomer has special needs which make conforming impossible
People going on and on about autonomous education being the whole point of home ed, only to learn that the newcomer follows a very prescriptive curriculum
People urging a newcomer to try out particular tutors and expensive activities when the newcomer is on a MUCH tighter budget than themselves
To the newcomer who is the victim of such gaffes, it might seem that they really don't fit at all, and in fact maybe that particular group isn't right for them. I hope they try a few more and find friends!