Of the Ivies, I would say Brown and Yale are considered the strongest in training and opportunity. Although non -Ivy, Northwestern is known for its theatre program. Northwestern didn’t require an arts supplement but my daughter just provided her monologues in a link and they did look at it (she graduates in a few days btw!).
For the Ivies besides Brown and somewhat Yale: You will find Ivy grads in many roles on Broadway, but that doesn’t necessarily mean the training brought them there.
First, there are many young people who are already actors and already represented who attend Ivies for the education. They will get placed regardless.
Second, the young people may simply have been well placed, the right place in the right time, e.g. in Columbia in the midst of NYC and making the most of the opportunity.
Third, the Ivy student may take advantage of a top internship or summer program but this you can do in any college, although perhaps the Ivy transcript made them more competitive (maybe, maybe not).
And finally, the Ivy may have a connected professor or director teaching a class or directing a student play, who by chance happens to need someone like the student for a show he/she is involved in. This can definitely happen, but it’s not a formal part of the education.
Your son has to ask himself why he is going to college. If he is going for training, he should ask himself what type he wants. Different Ivies are different in the types of training they offer. Take a close look at the curriculum. He should also ask what opportunities the college offers, if it has ties to an equity house and/or the broader theatre community, if it supports additional training in the summer or abroad, and what kind of internship opportunities and supports it has.
If he is going simply because he wants a great education and incidentally wants the chance of theatre opportunity but not necessarily rigorous and broad training, he would have a wider net.