No, not forever. You will probably have to brood them separately, because ducks grow much faster than chicks and they bulk up so much their curious or playful billing is one thing that can create havoc in the brooder with chicks. Plus, the ducks need a different watering system, since they dunk their whole bills into the water with food to sluice it around. Messy. Then they fling water around in the brooder and make it really damp. Easier to clean out just the ducks' brooder more often than deal with damp chicks.
Ducks - especially ducklings - bill EVERYTHING, even more than chicks peck at stuff. It's a curiosity behavior. Then a way to herd others around, get them to move out of their way, check out their feathers or feet or just anything about them.
I have two adult Cayugas, a pair, and after they matured, they stopped bothering the chickens.