I love broody hens hatching babies. We still have 2 silkie-mutt hens that were a surprise hatch a couple years ago--now one of them is the main incubator.
My mom doesn't want ours to hatch any more chicks and collects eggs from under them immediately, but she decided to put the duck's eggs under them instead. When I last visited home a couple weeks ago, I candled everything and the duck eggs were progressing! But I visited this weekend and when I asked about them, she said that a while back my dad collected everything from under the hens, including the duck eggs, ugghh. They sat out at room temperature for at least a day before getting returned, so don't know how much that will affect their chances.