sending letters of rec

Not usually, no. Are you sending the letters out directly to the medical schools? Often the secondary will ask if you have waived your rights to see them. If you are sending them out for your professor make sure they are originals (preferably) or photocopies of originals with his signature and on official letterhead/envelope so they look like they were sent by him.

 

They key is that the professor needs to have a copy of the waiver. Most likely he won't want it or care about the waiver, but it is to him that you are waiving your legal rights.