I haven't checked the item but based on how it likely works:
So Hex sets a status boost on an enemy. I don't think the passive set by the item would proc the extra damage as it works when the spell is cast. And hex doesn't do damage when it is cast on an enemy.
Maybe it needs a clearer description. When you cast a non cantrip spell which deals damage and you have...it deals an extra 1d4 of force damage.
