I only have one drake, and he ends up being out with a full grown turkey, or he's alone. He's only with the chickens for a short time, and there is a lot of space for them to scatter. He is mostly concerned with his mate, who he isn't allowed to be out with anymore, because he's too rough on her. So he visits with her through the chicken wire fence. If they were in close quarters, I might worry more. I would worry about him mixed with the OTHER ducks though. He doesn't like the 2 other duck hens. He tried once to mate with the turkeys when they were about the size of a chicken. I guess it depends on if they are an aggressive drake or not. Some people on here say that their drakes are "sweet". Not mine. He doesn't like me. He did act different a few years ago when we had tom turkeys, he seemed just fine. After we processed the toms, he went nuts on us. They've had this living situation for more than a year, and no chicken injuries.
My one drake is sweet, the other a touch of a pain not aggressive to people though, that i don't tolerate. It does depend and that is the problem, so best to raise the flag about the concern.