When Haka destroys an environment card and puts it beneath Savage Mana, does that trigger the draw ability of Dominion? What about when Haka uses Savage Mana and destroys the environment cards contained beneath it? Does he get to double-dip?
Yes, and yes. He gets to double dip. As does Bunker with Ammo Drop. Savage Mana has the funny effect of letting cards be destroyed twice.
Things beneath things are still Environment, Hero or Vilain cards (and come from the same deck, e.g. it's Tempest's hero card), they just don't have any text or 'sub-types' (e.g. Ongoing or Target) on them. Anything that triggers off of 'card type' destructions triggers, anything that triggers off of 'card sub-type' destruction does not.