Of course there is nothing wrong with breeding for ornament. Many dog breeds are bred for exactly that purpose.
I would say "most" these days. So many breeds have essentially lost their original purpose, although some individuals seem to have retained the traits of their breed more than others. This is exactly why Sheepdog associations fought so hard to try to keep Border Collies out of the breed ring!
If you think about it, from square one Basenjis were selected for "pretty". Most imports would have been chosen for what the eye sees, not for performance as a hunting dog, which would be unknown to a short term visitor. And I am sure the owners of the village dogs would be more than happy to part with a pretty but less talented dog instead of their best hunter.
It's good that Basenjis, along with other breeds, compete in contests outside the breed ring, such as lure coursing, but very few people hunt with them anymore, and that is where you would see the abilities they were bred to use. And whether they have lost them.
Registration papers should be proof, but without DNA confirmation one can never be positive. I know a breeder (in another breed) who was getting old and a bit confused and I am sure some of her pups' parents were not accurately attributed, but the pups were purebred, just possibly from different sire. Coat colour can vary tremendously and it's more likely when it isn't a disqualification in the breed. If you are buying a dog described as purebred then there should be registration papers given to you. A DNA test should tell you whether the dog is Basenji or mixed with something else, if you really want to know.