From Documentation, ( and if I get it correctly ), you will be deleting a particular item for a particular user. It will be the same way to delete any item within the user's box using the item-id and so my thinking is that it will be limited to the user. Its not a clean method, I agree , but its not supposed to be.
To keep a track , you could take a REST dump *before* you go on a deleting spree. See here :
REST update » Zimbra :: Blog .