I would assume the majority waive their rights. The only reason to see it would be if you were worried or not they were going to write a good reference. I'm not on an admissions committee so I'm not going to pretend I know for certain, but I would assume it is frowned upon. Also, they may ask you about it in an interview.
I waived mine. A couple of my references showed me what they wrote anyway (afterwards, in person).