If I have a Leyline of the Void in play and my opponent activates his Oath of Druids, are all cards revealed removed from the game, even if my opponent reveals a Gaea's Blessing at some point before revealing a creature card?
For the second question, they are all removed. Blessing has a triggered ability, but Leyline's ability creates a replacement effect. So you replace "put them into your graveyard" with "remove them from the game". Since Blessing triggers upon being put into the graveyard from the library, not being removed from the game, it never triggers.
