Normally if a wreck is not in the LOS of a unit it does not create a hindrance for fire through that hex. Would the same be true for the smoke emanating from a burning wreck?
Smoke fills the entire Location (plus levels above), so LOS is always hindered. This would even be true if the burning vehicle was in bypass of woods/building with the firer attacking a target in bypass of the opposite side.
And smoke generated is normally four levels high (two if Mild Breeze, none if Heavy Winds), so if the wreck is in a blind hex, its smoke can hinder fire nevertheless (B25.2).