In some type of odd scheduling thingamabob, Games Workshop released Ork and Tyranid FAQs from the Spain website first. The Ork one looks like its settled the Deff-rolla tank-shocking argument once and for all.
Tyranid FAQ (dated January)
Ork FAQ (dated February) UPDATE: English FAQ Now up
Here is the key Deff-rolla passage: (ruling in favor of affecting vehicles)
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
-Time to fire up babelfish everybody, and watch out for those now nastier deff-rollas!. We would be most appreciative if out Spanish readers could help us out in the translation department in the comments. You just know this is going to affect the meta-game…