If they can get into the coop at night I would think so. They're not really day hunters but I've certainly seen owls flying during the day, so if there's a target of opportunity.... If your chickens free range or have an open topped run they're vulnerable to any aerial pred.
Owls are generally night predators so they get them in their sleep. If they are cooped up at night then it shouldn't be a problem.
Depends on the type of owl. Great Horned owls have been known to go into a coop for chickens during the night so make sure the coop is secure. Also while they usually hunt at night they can be active at dusk and dawn and will hunt on cloudy days. I doubt too that a dog would be much of a deterrent--they'd just fly in and out over them. Netting over the chicken yard would be the only aerial protection.
i watched an owl take my leg horn rooster that was huge right at day break 4 years ago it took a few hens 2.they are very strong an fast an great hunters.
