Yeah, they use real snakes but as Lilie said, the snakes' mouths are secured shut.
Dogs don't generalize very well so you kind of have to use real snakes!
The training I did had a combination of an e-collar and then positive reinforcement for ignoring the snake. It's actually been really easy with all my dogs, as mine have had a natural aversion to snakes that is just tested/reinforced with the training...not sure why they are, but I've just been lucky. Some dogs at our classes have taken a lot more training.
You train initially with an e-collar, but then you test it without the collar. A good trainer will be really thorough about that. There are other methods of training that don't include an e-collar, but I think it's the easiest and most humane that I'm aware of. Since snakes are really appealing to dogs, you have to teach the dog that going after them is unpleasant, basically.
The training I went to wasn't particularly harsh. The collars were adjusted for each dog and the shock wasn't overdone. I'm sure it varies a lot from trainer to trainer, though, just like anything.
I sent an email to my friends in CO and will PM you when I hear back from them.
As far as SAR stuff, we don't carry anti-venom or anything. We learn about first aid and how to treat a rattlesnake bite, and we do rattlesnake aversion training as a team. Plus, the dogs are either in your sight or they're working and hopefully ignore distractions from snakes.
Really though it isn't something I worry about that much. If you're in control of your dog, the odds of any given encounter resulting in a bite are minimal. The kind of rattlers you have in CO would rather just scare off your dog rather than bite, so unless you let the dog antagonize the snake, a bite is really unlikely. Even if a bite does occur, the majority of bites by western diamondbacks (which are most of what you'll encounter in CO) dry bites where very little to no venom is injected. Of course the puncture wounds alone still require a vet visit, but it's not immediately life-threatening in the way a venomous bite is. Of course that's not to say rattlesnakes aren't dangerous, but I don't think most dogs necessarily need aversion training to be safe. The only reason I got it with my dogs is that I was living in an area where there were tons of snakes (seriously, on a half-hour hack I once counted 37 rattlers), and I was working horses so my dogs were out with me but I wasn't necessarily paying close attention to them. If I was just hiking with dogs, I personally wouldn't worry about getting the training or the vaccine. JMO of course.