Yes, some manufacturers produce 'poultry' crumbs / growers (like Allen and Page, Smallholder feeds, Marriages) that are non-medicated and suitable for ducklings.
For adult ducks, they should have roughly 50% wheat - if you feed layers pellets ad lib, they will take what they need. Drakes need more wheat and less calcium from the layers pellets. Ducks need the Calcium to lay.
Feed a little wheat with growers pellets to reduce the chances of Angel Wing (this reduces the daily protein intake).
You can usually buy straight wheat cheaper than mixed corn - and if there are chickens around (or vermin) it's best to feed it under water. I feed mine in a bowl with at least 3 or 4 inches of water on top. It's best not to let chickens have more than a handful of corn each day.