Gosh, it does seem that a lot of us have highly intelligent DCs with SENs!
Mine also does not like to disclose his diagnosis and certainly did not mention it in his personal statement. I do know that the school referred to it in their reference however. Also, when he was invited for interview, I contacted the college explaining the help he would need to navigate the interview process and they could not have been more helpful in putting in place support for him.
As a point of contrast, I have an older DC also with additional needs who has point-blank refused to seek any help for his problems whilst at university. Frankly, this has resulted in numerous crises, many of which could have been avoided if only he were more honest about his situation.
I fully understand the disappointment of Coleoptera's DS who felt he had met a good social group. Do tell him that two-thirds of the people he met and got on well with, will not be going to Oxford. They'll be going to the other top universities for his subject. Assuming he has offers for those universities too, he's likely to meet them again or at least lots of people like them who are also enthused about History.
If he liked the college environment of Oxford, the other universities which offer a similar experience are Durham, St Andrews, York and Lancaster I believe.