They don't have the right to trespass on private property without a warrant. These cops are a**holes. There would have been no "need to protect themselves" if they hadn't sneaked into someone's yard and woke up the dogs. The dogs were doing their job, protecting their owners yard, the cops are totally in the wrong here and I would say from most of the dog shooting articles I've read that most of the cops involved in the dog shootings are in the wrong.
Actually they do under exigent circumstances (which in this case apparently came from being chased by dogs - the second cop has a right to enter anyone's neighboring yard while in flight from a menacing dog.)