Ok so if they use the curse/cov as an enhancement in battle DoN can target it. Just to clarify. I did not think of that.
Yes, that is what is being said. It is because the card is a covenant or curse regardless of whether it was activated as an artifact or played as an enhancement.
Using a curse as an example but same applies to covenants:
Just like other dual alignment cards, once it is played as an enhancement, it “loses” the artifact side but is still is targetable as a curse because the card type is a curse (but could also be targeted as an enhancement at that point).
Conversely, once activated as an artifact, it “loses” the enhancement side but is targetable as an artifact (or curse). On a related but separate note, while it is active as an artifact, it is a neutral card since artifacts are neutral and the enhancement side of it is “lost”.