Most Duvel clones that I've seen require clear candi sugar. It's a waste of money to buy candi sugar over normal sugar in my opinion. The corn sugar will work just fine. The reason it's added to the secondary is so the yeast isn't overwhelmed right off the bat. I don't think it's a process that's real neccessary, but somepeople seem to think so.
__________________ He who drinks beer sleeps well. He who sleeps well cannot sin. He who does not sin goes to heaven.