Rumple has been proven NOT to be Zelena’s father because she had to use HIS blood to get past the blood magic seal on his safe in the shop whereas she used her own blood to get past Regina’s blood magic.
Zelena doesn’t know he’s her real daddy. So she would think she needs his blood, yes. Even if she did not.
And that kiss. It is just a paralel to Cora who sealed their deals with a kiss. .. Besides a certain someone is wheeling a knife to control him… A kiss is not incest. I too kiss my dad… though not like that…But they already said this wasn’t your standard Disney and they were gonna push the bounderies. So to me that kiss means nothing