If all the scammer wanted was email addresses, they could have written a random yahoo email address generator on their own. They want legitimate email + password combos.
Given that world + dog has the entire Yahoo DB by now, I wonder if a list of yahoo username + password still has any value on the market... Well, I can only hope so, or else the scammer will just drop all the yahoo addresses from his take rather than try to clean up the data.
If you can somehow find the yahoo DB, I will pay you $5000 in bitcoin for it :)