However, at 5:37, except that he moves back away from uke instead of dirictly adjacent, his throw is almost exactly how I have been taught to do one variation of morote-dori kokyunage in the Shingu lineage (Hikitsuchi > Mary Heiny > My teacher).
I would agree! That is a classic example of morote dori kokyu nage!
It is hard when comparing Daito ryu and Aikido syllabus, because as time has gone on, much is shared between the two. With out a historic written account of the techniques it would be hard to say for certain that they didn't both start showing the appearance of morote dori at the same time. But it is a good idea, what is the oldest written account of Daito ryu? That might at least give us some ideas about a time.
Thanks for the great replies!