Unohana's Zanpakutou never materialised in the Soul Society acc. She presented her shikai, that flying thing that carried the injured lieutenants after Ichigo rescued Rukia. Also you have to take in account the Zanpakutō Unknown Tales arc was not created by Tito Kubo, it was anime only material. That's why Renji's is an ape-woman and a snake boy rather than the manifestation from Soul Society arc of a baboon with a snake tale.