Does Wildfire Eternal give Dread Wanderer graveyard flash?
No, you can't do that.

When an activated ability says "activate this ability only any time you could cast a sorcery", that is placing additional restrictions on the normal rules governing when you can activate an ability (normally, when you have priority).


  307.5. If a spell, ability, or effect states that a player can do something only “any time he or she could cast a sorcery,” it means only that the player must have priority, it must be during the main phase of his or her turn, and the stack must be empty.