its not an assumption. Oryx, FATHER of Crota, the Taken KING, WAS born Aurash, Daughter of the Orsmium King, SISTER to Sathona and Xi-Ro. sexual organs are sexual organs in any species, and by the distinction of "male" and "female" being made, we can make the FAIR assumption that mechanically they are the same as we humans know them. now after that if females in Hive society act in a way that we would describe as "masculine" and so-fourth, vice-versa, etc, THEN thats something else entirely, could be like you said. but so far, functionally, female is the one that pops out the youngin' while males contribute genetic material, and Oryx is known as the FATHER of Crota. ergo, Oryx is a post-op transsexual (but in this case, the nature of that "operation" is unknown, but obviously different to the crude re-sculpting of flesh that we humans practice, as Oryx was able to produce offspring, therefore indicating fully functional sexual organs. unless of course, theres something that wasnt mentioned.)