"Back to my question, does splash damage from a cruiser shell get blocked by dead buildings?"
I can't say for positive, because I have not yet tested for exactly that scenario.
Not to mention it would be a real bugger to test.
But my best guess, yes, dead buildings will stop splash damage.
Shooting at buildings with 75mm he every 2nd or 3rd building only takes a single hit (instead of 2) because of splash damage, I see no reason why it would be different with bigger guns.
So if building is up, it will collect splash damage, make it easier to kill next shot.
Building down, prevents it from hitting the next building.
I could be wrong, but I don't think so.