They do all the damn time. I knew so many people at my undergrad (top public school in usa) who were waitlisted and got in anyway. Most of us gave applied to multiple schools, and get more than one acceptance.
I am waitlisted at one school because their admins fucked up processing my application (if it is so hard for you to track your own website and CSDCAS application at the same time, make it one single thing). I sent them screen shots of their mistake, asked for clarification, they stopped contacting me, and put me o their waitlist two days later.
I was since accepted into a much better program. I pity the fecklesd and arrogant admins at the other place if they take me off the waitlist, lol.