It would only seem fair to assume that Stardock employees are eligible for an Alpha slot. Although I don't think they would have to sign a NDA. More like, 'they already signed an NDA'!
Brad doesn't need an NDA to control what Stardock employees say, he has bees.
But seriously, there are lots of professions that have a built-in NDA. For instance, translators tend to sign one that refers to all the work they do for clients at the same time as signing their employment contract with a translation agency. I imagine any job that involves trade secrets/intellectual property/insider knowledge would have something similar.