I do not believe so, otherwise we would've signed one (even if it was a little check box). And considering this is a public beta I don't think so. AAAAnd in the past Stardock never did anything when people posted screenshots and videos from the public betas.
So I'm 99% sure there was no NDA that I forgot about for the public betas, but it couldn't hurt for a response from Stardock on this one