A card that discards a card "in opponent's territory" could discard a face down artifact.
The REG seems to disagree, if I'm reading this right.
Face Down
Face Down cards are cards in territories, battle, and set-aside areas that are face down either due to special ability, or are inactive artifacts in an artifact pile. Face down cards have no abilities, brigade, titles, or identifiers while they are face down. The only known attribute of a face down card is the card type.
Face down cards are only targetable by abilities that specify they can target face down cards or inactive artifacts, or cards that can target any or all cards in a location. When a face down card enters battle, it is immediately flipped face up, unless otherwise specified by the special ability that flipped it face down.
DtT doesn't meet any of the bolded criteria, so it shouldn't be able to target a face-down art.