When your son or daughter applied to The University of Montana-Missoula, they were required to demonstrate to admissions staff that they, indeed, met the admission standards for this institution. They provided their high school transcripts, college entrance scores (ACT or SAT) and any other important information about themselves having a bearing on their potential to succeed and contribute to the University's diverse campus community.
If they have already been accepted to the University, then they have demonstrated that they are, in fact, qualified individuals, despite having a disability.
This is different, of course, from the way things were when your student entered public school. Whether or not you knew of their disability at that time, or whether they acquired a disability later didn't matter. There was only one qualification for entry into public school -- as a child of the appropriate age, they were entitled to learn to the best of their ability.
None of us would argue that every person is entitled to attend college and receive a bachelor's degree. We would no doubt agree, however, that any individual who meets admission standards should have an opportunity to earn a degree. For the most part, disability is not part of the process of determining qualifications. Following admission, we would expect that each individual would continue to demonstrate that they are otherwise qualified by meeting or exceeding the academic standards set by the institution, and they must do so whether or not they request accommodations. (See Expect Access on Student Responsibilities.)