I can't speak for the specific schools, but I'll say that in general, many students here say that there is flexibility if you realize you want the other degree. It is usually much easier to move from the BFA to the BA, instead of the other way around (because of the audition, and also usually many more required courses).
At many schools, being able to adjust what you are doing - whether BFA/BA, or adding minors, or whatever - is part of the educational process. Some schools have very defined tracks, but even at schools where the programs are absolutely distinct, for example at UMinn, people do move among them. My D did apply to one school that had an auditioned BFA, and what we found out was a BA with an interview, and she could have messed up her application by neglecting to get the interview done in time. As it was, after the BFA audition she decided the school was wrong for her, but it did take some paying attention to make sure she had both options available. I think in this case, you and your S are going to have to read websites carefully and ask a lot of questions.
If your S can see the benefit of both kinds of program, just have him apply to schools that will give him various options in the spring. My D had a combination of auditioned BFA, non-auditioned BFA, auditioned BA, and non-auditioned BA in the end, and she took the whole year to decide what appealed to her most. With asking lots of questions, and doing a lot of thinking, (plus with the help of many wonderful CC folks), she made the right decision in the end. But the most important thing in the fall of her senior year was having a well-balanced list.
Some kids are more single-minded, but I'm guessing your S will want to have the variety of options. The only possible negative is that many kids don't want to go to a school as a BA where they were rejected as a BFA. I could see where that could feel strange for some people.