Access to NAS mount during Power Nap wake up
No - Power Nap is extremely selective about what activities it will take on and thus far, no third party hooks or API is provided by Apple to allow someone to easily modify what happens when the OS wakes from a nap.

Clearly, someone could reverse engineer things and come along with a solution, but that hasn't happened yet. If they do, we can surely come with a better answer but at the moment you get the behavior out of the box which isn't going to accomplish what you ask.