Yep. Depends on the breed and temperament of the dog. Many of my customers have dogs, as do I. All terriers (staffies, foxies etc) are a risk as they are bred to catch and kill prey. That being said, I have quite a number of customers which have had no problems at all with these breeds and their chooks.
I recommend that the interaction between new and existing pets be supervised, regardless of breed or species. One way to rectify problems (and keep the chooks) is to set up a hen-run. Most dogs are fine with chooks if introduce under supervision.