the only issue I can see with his past is if he is chipped, the vet may call the previous owners. vets have the latitude to just change the owner in the pet chip data base if they want, so the history of feeding and saving this dog from being killed by coyotes may have value.
another way to play this is to take the dog in for a check-up and shots. then if the previous owner is called they'll be on the hook for the vet bill and would probably give the dog to ya rather than pay the bill.
