i've recently taken upper-division/graduate courses in math, stats, EE and CS at three different US universities. 100% of the courses used piazza, because professors and TAs don't want to pollute their inboxes with questions and most questions end up being answered by students. it's not great, but it supports latex math (!) and its discussion features are much better than canvas (which tends to be the default, officially-blessed system these days).
membership in courses (and hence institutions) is usually managed by the instructors based on university email. "social network" features are pretty basic (based on courses, institutions, and contacts) but definitely exist.
i imagine the main draw for employers is that it's a nearly universal pool (for certain majors) of opted-in university leads with relatively reliable major/institution/coursework data for filtering.
"raid" might not be the best word choice, but given that students "have to" sign up to get course help and will probably manage to click on the opt-in careers button at some point, i can kind of see how people can see this pivot as skeevy.