Seeing old classmates on campus can be a nonissue. Eons ago I actually has a HS classmate in a small Honors Lit class but we never spoke et al- we were from the suburbs of Madison. The campus is large enough there are plenty of new people to meet and see. Given the huge number of courses, majors, buildings, dorms it is not at all like HS. I did not want to go to UW, I wanted to get away but finances dictated UW. I discovered a whole new world. Likewise son from a different WI city did not associate with hometown people but instead had his own life.
Do not let the fact that many HS classmates will be there influence the decision. Even coming from Dane County is not a reason to avoid UW. Every student has their own experiences- even having a parent who is a UW grad is not a reason to avoid it. Save the money.