Grandparent's question implies to me he's aware of that, and is wondering how much traffic AdSense drives on top of the DART stuff.

You can traffic AdSense through DART, so it is possible that the number has already been inflated with some AdSense numbers.

I think it's fair to count those though. If you have a DART tag on your page, the request needs to be handled by DART's ad server regardless of if it returns an image or a redirect to another network.