The Square Enix community reps who would actually be the ones to confirm it are at PAX East. They might have gotten approval face to face, but it's more than likely someone who wasn't suppose to give approval did. I mean, why tell a handful of YouTubers that it's okay to announce their involvement and not every single person and company invited? RSVP hasn't even ended, there's still another two weeks before all attendees have confirmed or rejected their invitation.
I think it's quite clear that I don't think highly of the Youtubers. I personally find their content pointless, exaggerated, over the top, and their personalities just down right annoying. A lot of them time they don't ask permission to use the content written on KHI or KH13, and just spend a video reading what was written. Sometimes they don't even acknowledge that it comes from there, or they use our translations but go to the source to avoid giving proper credit. Plus their voices....
I also found it quite annoying that they are, or at least were, making money from their videos but they recently put up one where they were going to get people to pay for TheGamersJoint's flight and accommodation to E3. Meanwhile I've never been paid for seven years of freelance work in the KH community and have paid for a plane and a weeks accommodation to LA out of my own pocket. No begging required on my part. Seems that idea has been thrown away since he is going to this preview thing, which means he might have been able to afford it all along and just wanted a free ride.