On paper he is, biologicly no. No blood relation what so ever.
The biology of the situation is irrelevant. What matters is the legality. Legally, your husband is the child's father, and legally, he's the one who must consent to the step-parent adoption.

In the area of form ADOPT-200, where you're asked to name the child's birth parents, the names should be those of the parents on the birth certificate. As far as the courts are concerned, since your husband signed the birth certificate, he IS the birth father.

If he cooperates with the adoption, his rights and responsibilities towards the child will be completely severed, and the child's birth certificate can be amended to reflect the new legal parent's name. Read here.