I'm a newbie to hatching (just hatched my first two days ago!) but I've read ALOT of books and posts on chickens.
From what I gather, it is ok to wash them before hand, but use warm water. Cold water can make the shell contract, apparently, and cause bacteria to enter into the egg.
I did not wash the eggs of the chicks that I just hatched (from my own chickens). But, I did just put three more eggs into my r-com mini and those I did wash. We'll see if it makes any difference.
I think it's probably best not to wash them, if possible, and to use eggs that are naturally "clean" and free of dirt/feces/etc. I remember reading somewhere that the eggs have a natural coating that protects during incubation. I am also reluctant to use any chemicals in the cleaning process, since eggs are porous and I wouldn't want anything absorbing into the embryo.