The difference between wheels and exhaust tips is similar, but not quite the same. The wheels get warm, but an order of magnitude less than exhaust tips. When braking the dust is hot, and the wheel protection will be the sacrificial layer. The exhaust tips on the other hand are expelling the gasses as a result of an explosion, and get much much hotter, and is essentially at the same hot temperature the entire time your car is running. Wheels cool down when not braking.
Wax on exhaust tips is a total waste of wax once you have gotten your car up to operating temps...it disappears. Carnuaba even sooner.