The total rule against dogs is a relatively modern interpretation in islam. It isn't even to do with the dogs themselves, but that most dogs were smelly and unclean creatures. There is plenty of evidence that the ban really only applied to mongrels, unclean street dogs. Working dogs (hunting/herding/guarding) particularly those similar to salukis, were not considered unclean and were kept. The Quran specifically states that animals caught by trained hunting dog may be eaten (005:004) with the necessary implication that they may be kept and trained.

The fear of black dogs is very much ingrained in many Muslim countries. But that tradition predates islam altogether and is widespread even in the west (black dogs are far less likely to be adopted).