Probably not. It is a very common breeding practice with purebred dogs to "line breed" or breed related dogs to strengthen a particular genetic quality. So you will not see negative, "banjo - playing," interbred qualities in one breeding but if dogs are left to only breed among their close relatives generation after generation, you will see health problems emerge.

Now the bigger issue is, are you making plans to have both dogs sterilized? You can have the puppies aborted by a veterinarian if you feel OK about it, but since these are not show dogs, please be sure the male is neutered immediately and that the female is spayed as soon as possible. Pit Bulls have large litters and there aren't enough homes for the dogs already on earth. Another litter will just be that many more dogs to find homes for and Pit Bulls can be very difficult to place. Take care and thanks for saving the dogs! I have six rescue dogs myself and love every one of them - and they are all spayed or neutered! Good luck!