Hey,
Snapback says in part “It can’t be summoned until after its owner’s next turn.” Blackhand Resurrector says in part “Summon a hero from your command zone.”
The way this works in general is that text on cards beats text in the rulebook and text that says you can’t do a thing beats text that says you can or must do the thing. In this case, “It can’t be summoned” on a card (Snapback) will prevail over any other card’s efforts to summon the hero.