1.) I was at White Mountain as part of a tour group. We were allowed to walk among resting dogs, but told not to bother, touch, or feed them treats without the musher being present. Anyone could have done it; there were volunteers wandering around supposedly keeping an eye on things, but it was haphazard and many times the entire rest field was unwatched. Heck, you could simply throw a small treat at a resting dog when someone's back was turned and it would be vacuumed up within a millisecond.
2.) The "prove you didn't do it" rule is not workable logic - it's impossible to prove a negative, and not allowed in law (think the Salem Witch Trials). Someone on the Iditarod committee please take a college-level course in Logic, and in Statistics/Probability. 
3.) Mushers: never have a conversation with a race representative, for any reason and at any time, without recording it, and telling them you are. If you don't have it in writing/recorded, it didn't happen.