Well D by G is in the Vehicle and assault rules and it does say 1 attack be it gun CCQ or grenades. But it does say that it automatically hits. Also D by G can only be done if the vehicle is doing a Tank shock move which means it must make contact. This may be a good tactic for WF as Tank shock is a movement thing and the effected unit move still be in cohesion and only move the shortest distance.
Tank shock,WF ,living vehicle, assault.
So WF vsD by G if D by G is done the attacker hits but then get flamed to death no matter what.