Underage drinking is a civil offense in Wisconsin, not a criminal offense, so that probably explains some of the seemingly low arrest numbers, but disciplinary referrals (basically school issued tickets) are much larger. On page 9 of the 2018 Clery Report it shows that on-campus there were 2,190 liquor law disciplinary referrals (first two columns combined) and only 1 arrest, and 729 drug disciplinary referrals (13 arrests). The Clery Report (federal law requires all higher ed institutions to complete annually) does standardize reporting across schools, yet even then there are differences in how arrests and violations are recorded and captured. Then, one has to do the math to get an incidence rate per 1,000 students. Clery report also captures other crimes such as rape, burglary, assault, domestic violence, etc.
http://uwpd.wisc.edu/content/uploads/2018/09/2018-ASR-FINAL-9.28.pdf