I've talked to some students recently who've told me of a few new entrances in exchange for the complete map of the tunnel system that I just happen to have
Basically, the tunnel system is split into two sections by Emmet Street. Each section has a few steel gates at different intervals, blocking access to various parts of campus. There are also gates blocking access into buildings.
Students find tunnel entrances by walking around campus at night, checking out every grate they find. Eventually, they usually find one that isn't bolted down and provides steam tunnel access. That's what I did. I'm unaware of any connections to storm drains or sewers...it's unlikely, but I've been doing this long enough that nothing surprises me anymore.
I don't know what would happen to a university employee caught in the tunnels. Usually it depends on the mood of the police officer.