Rob has officially ruled that Covenants/Curses are treated similar to DAEs:
"A Covenant/Curse is both an Enhancement and an Artifact, and can be targeted as either (in hand, deck, or discard pile) until it is played, held, activated, or placed in Artifact pile as one or the other. A Covenant/Curse that is played or held as an Enhancement can no longer be targeted as an Artifact, and a Covenant/Curse that is activated or placed in the Artifact pile can no longer be targeted as an Enhancement. They are still always targetable as a Covenant/Curse."
This ruling will be posted in an REG update thread, and now that the REG can be updated more easily, it will be added to the REG in the next update.