I have pugs and I never let them near them, I have seen the adults belly crawl through the garden poised to attack them even with me standing there. I always let the dogs out first thing in the morning for their time in that section of the yard and then bring them in to let the girls out to free range the rest of the day. The dogs then have to use the part of the yard on the other side of the fence if they need to go out, where I have to stay out and supervise them. After the girls are safely back in the hen house, I let the dogs run in the yard again. Tts a pain but the only way to be truly safe and its now just our daily routine.I can bring the pups out in the yard with the chickens and no one bothers anyone, these little guys are too little to even notice the chickens.
However, even though they are being brought up with them, born one day apart, I will never trust them alone with the chickens when they get older. I think any kind of dog is just unpredictable, not just the ones with the "bad reputations". My breed is not a bird dog or bred for any kind of hunting, yet I have to chase after them if they somehow get into the yard while the girls are out there.
I think sometimes we get a false sense of security because they seem to all get along, but then one day boom thats it.