I'm putting myself out there for someone to tell me I'm wrong... but, isn't "Earthdog" sporting/hunting typically done with short legged canines? I can't imagine a Basenji going into a dirt tunnel after anything. They might try to dig down and make the hole bigger, or stick their head in, but they aren't going into the hole. Their body structure just doesn't seem appropriate for this activity.
@beth314 - I think the issue with a Basenji doing Earthdog is that those dogs go underground to seek their prey.... (as in for trials they make tunnels and the prey is in cages at the end).... and that is not an activity that Basenjis really do. They might try to get to the prey by digging on the top of the ground, but going underground I don't think so.