OK, so I spoke with the plug in developer of Dolby Atmos at NAB in Las Vegas in April 2015. He basically said this:
Dolby has no intention of developing a Dolby-brand Atoms plugin for anything other than PT specific, because that is the only platform they see “professionals” working on. That hurt my brain to hear, and I tried not to act insulted as I expressed to him how far from truth he was.
I suppose you can mix to Dolby Atmos via their RMU hardware encoding unit, somehow, but good luck with the panning natively until a plugin is developed for “up and down” mixing that is compatible with the system.
We, Nuendo users, need 3D mixing options. Our native surround panners are SO good, already. To stay current, modern, competitive, this progression is necessary.