As game design related questions are more closer to the user experience when playing the game, one could need to allow access to a playable prototype.
But there is always the problem on how to avoid that information being disclosed.
Any question which is so specific to your situation as to require an NDA and access to one of your builds, would be considered too localised a question for archiving on stack exchange, and would likely be closed for that reason.
Additionally, why would people want to put themselves under a legal obligation to you in order to answer your questions, for no gain to themselves? If you're in a position where you require people to sign an NDA, you probably need to start actually paying people for their time and effort.