I got it too, and would also like to know the answers to these questions!
I do know some people at Duke who have other named scholarships which don't have a contingency clause, but I'm not sure if that applies to this scholarship.
I imagine that a lot of people who get the nomination don't even interview for it, either because it's too hard for them to get there to interview or because they're not seriously considering Duke, but I'd really like to know how many people end up interviewing and how many end up getting the offer...