I would say that I've never heard of a situation where tickling took place as PART of the initiation thing... but I can say it's happened DUE TO the initiation.
Hazing is a practice that no matter how hard you try to stop it, it will continue to be practiced here and there. And one particular method is to tie up a victim outside to a pole or some other thing. While it isn't exactly a common thing to see a victim attached to the some pole or bike rack or who knows what else, both frats and sororities are known around my campus to do this. And not always JUST for some sort of initiation or whatever else. And usually either involves being abandoned outside for a while (or at least made to think they were, with someone inside watching to make sure they are ok every once in a while) or involves some sort of food being tossed at them.
Now I would say, statistically speaking, the chance of these people being bound to some surface or another for at least half an hour or more and not having at least one yahoo come up and give em a few giggles is slim to none.
If I had to guess, I would say someone, somewhere, if not a few people have found themselves and tied and tickled by their sorority or fraternity.