Another commenter mentioned the police's vehicles get flipped by rowdy sports crowds. The vehicle is probably surplus from the Iraq wind down. Some of LAPD's helicopter fleet is, apparently, military surplus.
I would think that even if their MRAP is free the logistics would make it more expensive that whatever vehicle SWAT is using. I would think that an Armored car (like a bank would se) would also be a good choice if they're just looking for a heavy and protected vehicle.
Realistically, it seems like if the crowd is that ugly, the local PD should be called in. I don't think riot dispersal is really a great responsibility for campus police.
Re the mines: I'm guessing you don't get much of a chance to check for mines, especially on convoy routes. Car bombs at checkpoints (like the video I linked) are probably impossible to detect before someone is in the blast zone.