Well no, it specifically says it's a memorial - at that point it's a statue, like an art installation, especially if the tank is non functional(bonus question - what if it was never an actual tank in the first place, it's just some metal bent to look like a tank?). If the memorial was of a Napoleonic soldier on a horse, you wouldn't say it violates a "no weapons allowed" rule just because the statue is holding a sword.
If it's a real tank that just happens not to work any more then it's a vehicle even if it as a monument as well.
That completely depends on your definition of a vehicle. According to your definition an object that once met the conditions to be a vehicle will always be a vehicle. You can apply Theseus's ship to the WW2 tank replacing it's parts and then at what point does it seize to be a vehicle?
If your definition on vehicle depends on transporting humans than a wagon seizes to be a vehicle. If your definition depends on transporting objects in a self-propelled way than humans become vehicles.
Same thing about the WW2 tank that's not working. A vehicle that doesn't work is still a vehicle.
Also all the questions about verticality at least under my jurisprudence land is only owned vertically up to a certain extent after that is considered state property to be administered by authorities.