They don't know any spoilers, but they've worked ahead of time to release X-wing related material, which takes some time to design and produce, so it's not out of the realm of possibility that they've had some foresight into the species. The RPGs have often been the largest source of detailed information regarding species we see only a few seconds off, and only biggest of nerds (usually RPG fans) would care about the intricate details of said species history, culture and planet anyway.
I find it highly unlikely, sure, seeing as we don't know how long the book has been in the works, but not impossible.
New species, especially if they're relevant to the movie itself as opposed to Star Wars in general, would likely be spoiler information. X Wing and Ties are common Star Wars items. And it's not like I'm saying we'll never see material from the movie. I just don't think this is going to be the book where we get anything related to the movie. The next one they announce for this line? Sure that sounds more likely than this book.
