Senju and Uchiha are just water down Uzumaki, Why do you think happens when you combine Senju and Uchiha DNA, You make it back to what it used to be before it was divided, A unify DNA again.
as much as it is a possibility, don't forget Kushina mentioned that she brought from outside the village; meaning she had not been in Konoha all along. If she was Hashirama's daughter, then she wud ve been in Konoha.