I think it's all about a well trained dog and exposure therapy. When we first got chicks, our poodle was very interested. We would let her sniff them and watch them in the brooder. We had a tote with chicken wire wrapped around it so sometimes we would catch her laying with her nose pressed against the side watching.
As they got older we have let her sniff them and be around them, but always supervised.
Now the poodle is 10 months and then chickens are 5 months, and they tolerate each other pretty well. When our hens are free ranging in the evenings, the dog is outside with all of us. My husband and I will do chores while they're out and don't really worry. She still tries to play with them bc she is a puppy but she only wants to chase them. She will run into their area and they will spook and fly off. We generally call her down for that. As she is still a puppy, we don't stray too far, because although we don't think she would aggressively attack, we worry that she may try to play too hard.
Now, she is excellent at helping herd them back into the run. We can tell her okay, lets put them up and she will round them and hard them right into the run. Its actually comical.
Hope that helps!