I'm of the mind that regardless of your dog's history, breed, mannerisms, whatever, they should not be left alone with the chickens. Dogs will be dogs and I feel it's unfair on the animals (both chickens and dog) to underestimate your dog's most basic instinct.
As Accidentalfarm said, should a dog do what it's instincts are telling it and kill a chicken, would you be able to keep the dog without resentment? It's unfair on the animal to expect so much and then punish him when he does what nature intended him to do.
I'm of the feeling that my dogs were here first and I'm not willing to put them in a situation where I would feel animosity or dislike towards them. They are my babies and I love them dearly, but I know myself and know that should one get ahold of another one of my babies, I would not be happy.
My dogs will never be allowed out with the chickens unsupervised for any amount of time, period. We're still in the 'training' phase to see if it's even possible for them to coexist with the chickens while heavily supervised.
Many people argue with me on this, but I believe that whilst training an animal, the first lesson you are teaching it is to not misbehave in your company. They're smart creatures. Ever see a dog do something wrong when they think your back is turned, but they cower immediately when you get home even before you've seen what they've done? They know it's wrong and they know you don't like it.
I think the best possible outcome would be having your dogs behave with the chickens while you're around. I wouldn't strive for them living in harmony on an unsupervised basis. Like I said before, it's unfair on all involved, including you!