From its description the Death From Above Talent seems to be intended or designed to be used against a single enemy versus a horde. Based upon its use with a Charge Attack action. I am sure if we were to request a clarification concerning Death From Above and Perternatural Speed we would get a ruling similar to other similar talents, Thunder Charge for instance, which give a bonus to an attack. The ruling being, "The bonus only works with the first hit of the attack."
I understand what you are asking: Does it combine with the possible multiple attacks you get from extra hits generated by Degrees of Success. Based upon previous precedent I would have to say: Yes for the first hit generated, but no for any hit after the first.
If the talent mentioned smashing a multitude of enemies assunder, or blasting whole squads apart I would obviously support another decision. But the talent does not, its description infers it is intended for single targets.
Besides, it is probably hardly necessary. The enemies you are likely to face in a horde are more than likely so weak the extra damage is simply overkill.