Out of the 5,677 that were offered a place on the Waitlist last year, 2,126 accepted (you are not automatically placed on it). Out of the 2,126 students who went on the Waitlist, only 66 were accepted, which translates to 3.1%. While the percentage is dauntingly low, the fact that 66 did get in is very encouraging. Many other schools I checked in the past accepted only somewhere from zero to less than 10 off of the Waitlist.
There is a thread below for Lehigh RD Decisions where there are many more posts on decisions and stats which may offer everyone in this thread more insight.