if blood is needed to summon then how did hanzo summon his salamander and nagato his summoning creatures
Good question, its probably one of the lupines that allows edo's to do such thing. Or maybe since the edo's DNA was needed that's enough to summon without the use of blood.
i think they have both mastered summuning like how tobirama mastered suiton with one hand sign, they also mastered summuning techniuque (spelling)