I hunt upland birds with three dogs and worry about snakes quite a bit. The best thing you can do is to take all available precautions and cross your fingers. I would recommend both snake breaking and the rattlesnake vaccine. Neither are 100%, but either could save a dog's life. Once the dog is bit, it is all a game of chance. If you can get the dog to the vet soon enough, they can administer antivenin and save the dogs life. The problem for upland hunters like me is that vet clinics are usually hours away. It is still a good idea to take a dog in though, because vets can give the dogs steriods and fluids to help the dog through it. The location of the bite is also outcome-determinative. If a dog is bitten on the leg or back half of the body, the dog has a much better chance of survival. Bites to the rib cage, neck, or head are more likely to be lethal. Even if the venom isn't enough to kill a dog, swelling sometimes can. Dogs can and do survive snake bites without any vet attention. I know an old bird dogger who grew up hunting quail in Missouri. They would have bitten dogs every so often and none ever died. I also know of dogs here in MT that have died from snake bites.
Like I said, take all the precautions you can and cross your fingers for the rest.