First off, you don't activate Oath of Druids. It has a triggered ability, not an activated ability. For your first question, Oath's ability resolves completely before the E. Witness ability goes on the stack. So all the other cards revealed are already in the graveyard and are legal targets for the Witness's ability. On the second question, once you've revealed the entire library you simply stop. There's no revealed creature, so no creature is put into play, all the revealed cards are put into your graveyard.
I'm fairly certain I know the answer but :
If I activate Oath and the only creature in my library is an Eternal Witness, can I select a card for EW's comes into play effect if i placed in my graveyard via activating oath that turn?
My gut says no since the cards enter the graveyard at the same time I'd have to choose a target for EW and so they aren't there yet to actually target. Of course I could be wrong on that.
A second question: if I activate Oath and have no creatures in my library what happens ? ( I won't auto lose due to card draw during draw step because I run krosan reclamations to cast during upkeep).
The goal here is to dump my library and get yawgmoth's will back then storm for the win, I'm just trying to figure out if I should run a single creature or not.
