I never actually raised ducklings and chicks in the same brooder, so I can't help you there, but if you do try to attempt it, make sure to get non-medicated feed. Medicated feed can kill ducklings. As for keeping them in the same coop, my birds get along quite well! My drake was raised with chickens and has no problem with them, and the ducklings that are now outside in a separate pen are warming up to them. So I would think it would be easy for you to keep them together if they at least get some playtime together as babies. Watch out though - ducklings quickly outgrow chicks. And a rooster could easily get aggressive with a duck if he felt it was a threat.