They'd probably have quite a good reputation, so banning Digg from using Adsense isn't going to help Google Adsense.
what I find most interesting about this information is that Digg started out just like us: fairly small, and then expanded globally. so I guess it should be safe to say that nothing is impossible. which, in turn, inspires people like me to work harder for that same position.
They should earn quite a bit. Even if their traffic are mostly tech savvy and know about Adsense, the percentage that don't are enough to make them that much. Just imagine how much traffic YOU get when your articles get dug; now imagine how many people never visit you, but do visit Digg. The numbers are astounding. Even if 1% of them clicks on an ad, they'll still make 5-figures pretty easily.
With sites like Digg you need to be more conservative in the estimates - to be safe you need to consider about 0.1% actually do click. I am basing this off of the number of people coming from digg and actually clicking on any ad (a measure of how likely they are to click an ad)