It depends on the subject matter. I wouldn't expect someone on the spectrum to do well in literature or languages or any of the social sciences. But engineering or computer programming or something solid like chemistry? I imagine they'd do very well. I heard of one person who was handed a Ph.D. in economics for developing a computer program that mimicked the European market (circa 20-25 years). He had coded it because he was interested in the problem. That is classic Aspie behavior.
The problem is that in graduate studies so much of the work is done outside of class. Someone who needs rules and structure can't function well like that. However, it is not the business of the department to provide that. The whole purpose of a graduate program is to work outside the existing structure, paving the way for new structures, if you will.
The office of students with disability might help, but ultimately if his family thinks he needs his hand held, they will have to hold it.