I think people here are over thinking the question.

Quite simply... can a dog keep away a bear? The answer is yes, though I can imagine in certain circumstances a bear being drawn to a dog.

In my experience, I remember once as a kid walking through the woods. We saw what looked like a black lab further up the trail. My dog took off after it and we watched a black bear amble away (dog +1). Of course I was camping once with that same dog. She woke me up in the middle of the shaking with fear. It took me a little while to realize there was a bear outside our tent. She never said a peep (dog -1).