@ElizH - From experiences, a few things! We also have chickens and have raised them together fine in the past. However, our Khaki males tend to not only protect the lady ducks (we have a bully hen who used to be mean to our female duck) but also if you end up with all male ducks - they will go for the chickens if you catch my drift!
PREDATOR PROOFING. I cannot stress enough. If you have gaps in their nighttime enclosure, you risk losing them. We just recently had an issue losing our beloved female duck to a massive chicken snake. Set yourself a game camera or nest cam up on the pen or inside the coop to check out potential issues. We also get giant gopher rats trying to get into our feed, so try and keep feed contained where you can remove it at night and not invite little buggers in there. Where mice and rats end up, snakes follow. We also used to get raccoons and possum alot, but responsible trapping helps. That is a good opportunity to learn about tanning!
Remember, duckies love the water and love to swim. Have yourself a setup easily cleanable. =)