They really don't care who uses it, but that person is the only one who can use it that day. But, that's where the ink stamp comes in when you exit a park. They don't want four people sharing two passes,meaning two go in,one exits with both passes,two more go in,one exits with both passes, then two more go in. The machine remembers when the ticket first went in. when it see's the ticket come back again,it alerts the CM to look for a hand stamp. No stamp means someone else is trying to use the ticket on the same day.
At this point you simply throw a fit,scream about handsoap or pool chlorine,etc.. and they beep you in anyway.