I am not sure I understand the question a you phrased it?
If you simply want to play video off a NAS on a iPhone or iPad then you do not need to involve the ATV at all. There are av ariety of media payers for iOS that can play directly of a NAS. I for instance use OPlayer for this purpose, but there are others with similar functionality. Usin Air Play (which is standard ATV2 capability) you an get any video playing on the iPhone/iPad replicated on your TV.
The ATV2 gets involved when you want it to play media from your NAS on your TV without using your iPhone or iPad. That is where ATV Flash (black) comes in. It provides a Media Player that runs on the ATV2 and an play the media directly off the NAS.