I came a across a US group that rehabilitates dogs that were used in dogfights, mainly pitbulls. From memory, they claimed their success rate was somewhere around the 70-80%. Lots of those dogs were rehabilitated to the point where they could be trusted around other dogs, children and other pets and were rehomed in 'normal' families. A minority didn't quite get to that stage so would've required experience handlers, but were no longer regarded as dangerous dogs.
What a great job they do. And you too, newfsie.
A friend of mine is currently fostering a dog for the RSPCA while he recovers from an ear operation. Apparently this dog is so dog aggressive and such an extreme fence jumper, that she is only allowed to walk him in the backyard on a lead. I am desperate to find out what the RSPCA's plan is with the dog after this. He'd been at their kennel for about 18 months before they found a foster carer and could go ahead with the operation, and they apparently did not have much of an opportunity to try to rehabilitate him. So what will they do when he is recovered? A dog like that could only be rehomed with someone who is very experienced and totally committed to rehabilitating him and people like that must be as rare as hen's teeth. (He's not a pitbull. My guess is he is a staffy x hound of some sort.)