The allusions to Adam and Eve can be seen as a symbolic contrast to the central action of the novel. They are symbols of innocence in high contrast to the folly and violence of war and pettiness that characterize the novel at large.
Slaughterhouse Five is a novel about innocence in a way. The protagonist, Billy Pilgrim, is essentially an innocent bystander in World War II, send to Germany to play the organ.
Billy doesn't carry a gun and simply wants to give up as soon as things get bad for him. He doesn't want to fight back or conquer his enemies. He is not out to kill, not at all, yet he is caught up in the bloodiest war in the history of the world.
Adam and Eve stand as symbols of innocence when they appear in Slaughterhouse Five. They are described as desiring to do good.
Like Billy, these biblical figures serve as a contrast to the insanity and the bloodiness of the war and the bombing of Dresden. In a world where purity and innocence do exist - as evidenced by Billy and Adam and Eve - the tragedies of war seem all the more emphatic and distressing.