Dear All - the umbilical hernia as you say is very common in the Basenji and quite a number of the original imports into the UK from Congo had them. In many years involved with Basenjis I can recall only a handful where it was essential to have the hernia 'fixed'.
Sometimes the wall closes or gets closer trapping the intestine and then an op is definitely necessary. You can spot this is happening when the hernia gets hard so its really only a matter of keeping a watch.
Quite frankly it is my belief that many judges don't even notice them! (I'm speaking of the UK as I have no experience anywhere else!) Incidentally I always leave the dew claws on my dogs and in many years of showing I have had only one judge actually mentioning this!! I can only assume that they jsut haven't noticed.