This garb can be worn without equipping other pieces.
I do have a Reborn Shade helm in my inventory also. I cannot wear that, because it says I do not have all the pieces.
Not sure if there are more items in the set other than a helm & armor, because I have only seen those in great variety.
I can confirm that at least with the cloth armour you can not equip the helmet with it (tried 2 helmets in the set) only the armour on its own.
It's three items, see me after a reset to get a fixed version of the cloth.