Well, well, well... the Deff Rolla debate has been settled once and for all by an updated GW FAQ for the Orks.
Q. Can you use the Deffrolla when Ramming
vehicles or does it only work when Tank
Shocking non-vehicle units?
A. The death rolla does indeed inflict D6 S10 hits
against vehicles, as Ramming is just a type of
Best 20pts spent in the Ork army!
The full updated FAQ can be found below, although it seems like that's the only (very necessary) clarification: http://www.games-workshop.com/MEDIA_CustomProductCatalog/m970066a_2010_Orks_FAQ
There should also be a Nid update on the way :)
Peace out Battlewagon fans!