I have had just a little experience with this.
This may seem obvious but:
Always have the special needs person dance their gender. I have had
well-meaning partners put a woman with special needs (Down's) in the
man's role, and it makes it much harder for others to help them if
they get disoriented because the helpful person' s first thought is
to assume the special needs person is dancing their own gender.
Dances like the Virginia Reel (no gender critical) worked well with a
group of predominantly Down's Syndrome kids that I called for once.
Yes, it helps if the dance has a lot of connectedness and not walking
around by oneself. Even a do-si-do can be disorienting for a special
needs person, as opposed to an allemande.
I have had a couple of people that I am aware of who had borderline
autism come to the regular dances. They really enjoyed it and came
back many times. I think the good thing about the contra situation
for people with this condition is that the social interaction is
prescribed - they know exactly what to do with the people they meet,
star, do-si-do, swing, etc., there is structure, there is pattern.
Often open-ended social interactions are particularly difficult for
people with autism, and the social interaction during dancing in
contra is defined for them. Of course, it could be more difficult for
those with more severe disease.
Be flexible, and have a good time!