What everyone replied with sounds correct to me.
A similar example I can think of is Helm of Fear for the Warlock. It's technically a defensive roll, but it never SAYS it's a defensive roll. It just works like one. So because it isn't labeled as such, I can always try to Helm of Fear, then if that fails, use a Defense item/Enchant roll on the same attack. (Rules state only 1 Defense roll per attack)
So the cloak and chestplate work in the same manner. It's faking a Damage barrier without being one, letting everything work!