I suppose this thread pertains to forest grouse, but for what its worth, most of my experience has been with prairie grouse.
You can hunt these birds without a dog, but success can depend a lot on factors such as time of day and available cover. If i'm in a new area that is quite homogenous in terms of cover, I would hate to be there without a dog. Of course, success in this case is based on the premise that the dog is as staunch as a fence post.