NDA, sadly. It is ultimately best for the success of the game to comply with it imo.
No it's not. Alpha/VERY EARLY Dev is almost always under NDA but Beta rarely is.
Having only the opinion/feedback of a very small segment of your market in the form of Beta testers is never good. A large % of people who get into betas do so for having a blast and some fun and almost never submit any feedback whatsoever.
What purpose does keeping a beta of a game under full NDA when you have so many people in it and everything will leak anyway?
Public betas, which is what PS2 beta will be, invite or not do not need NDAs. Everyone and their dog just likes to slap an NDA on everything these days, gives them a get out of jail free card to censor anyone and everyone without lashback from the community for it.