Haven't ever heard of that happening in any of my local martial arts schools, almost all of them have a focus of building confidence and discipline next to technique and physique. I doubt the kind of martial arts you do matters, the real difference is going to be the teacher. I have been part of three different types of martial arts ( Karate, Kyūdō and a brief period of Kendō ) and all had very kind teachers.
If you happen to have a teacher that turns people away for having autism they likely aren't good teachers, so that saves you a waste of time. Just be upfront about it and see how they react, most are very understanding as part of what they are teaching is to build confidence and self-respect. The only real legit reason a teacher can turn you away for is if you are being overly disruptive. I have known some people with autism with very bad impulse control who could get very aggressive fast, such behaviour is not tolerated in a respectful and disciplined environment as it endangers other students.
