I think it is a minor deterent. I was out in the yard watching my friends free-range and the biggest hawk I've ever seen did a couple of flybys. I was waiting for it to go after my "oblivious" chickens in the middle of the yard before I sprang out and set the dogs after it. (No harmful intention toward the hawk, just hoped to scare it's tailfeathers off and make it fearful of the "predators" waiting for it in the shadows of my yard. LOL)
He came for a third flyby and seemed like he was locking on to a target(chickens were dissapointing me because they STILL hadn't taken cover) but then the horse who was in the backyard with the chickens walked over to where the chickens were and the hawk immediately changed course and dissapeared over the trees. (Horse was not "protecting" the chickens.. LOL.. they were standing in the tallest green patch of grass in the yard..)
I'm not saying that if he had been starving he would not have taken the chance, but it did seem like a "minor" deterent. I'm sure that hawks don't care for other animals(especially larger) moving around when they're hunting for lunch.
I don't believe it is specifically goats, I think any other larger animal moving in the same pen as a chicken will make a hawk think twice about coming in for a kill. You have to rememer, a hawk is most vulnerable on the ground, they want to make sure they don't become lunch when they come down.
I would not get goats just to keep the hawks away but if I had goats, I would let the chickens roam in the goats pen.
-Kim