Wow, you found a thread from February that interested you? Cool. How far back was it?
Giving out candy is against the new federal guidelines. Teachers shouldn't be giving any foods of minimal nutritional value. If your child's teacher does, ask her the official policy about foods of minimal nutritional value. If she gives you a blank stare, write it down and tell her to ask her principal and you'll talk to her about it tomorrow.
HOWEVER, that is only for public schools. Otherwise, ask what the center/school's policy is. You may have to deal with it, move your child, or speak with the director and change it for all kids (be prepared for them to refuse in which case go back to options one and two).
Asking for sugar free candy won't support your goal. It's not that that amount of sugar will cause a weight problem, it is the idea of sugar being a reward. Sugar free candy is still sweet. The children don't know the difference.