I never actually parked in the garages since they always had signs saying "full" (and long lines) and so I got used to parking elsewhere, but I'm pretty sure both of them (there were two at the time, but they were building another) were open to students. Certain sections for faculty, like the faculty sections of the regular parking lots, but surely there aren't enough faculty to fill the garages.
I didn't mind parking in the overflow lot, though generally I wouldn't have to after a few weeks. It's when the overflow lot overlows, and then the secondary overflow lot down the street overflows too such that you end up parking in the dirt near it, that it begins to take several days hiking and a GPS system to get to class. Luckily I took public transit four years, only had to park the last semester when I lived out of town.