Laaaaate reply. First post for me however, so huzza!
From what I could tell from the in-game context, Weyland-Yutani is clearly aware of Predators and has been for some time. Their existence has never been publicly announced however, and WY likes it this way. Whether or not the AVP movies' storylines are canon, The Company has made some form of contact with Predators in the past, or at least their technology, and may have even advanced their own R&D from Predator assets. I believe that since Predators are a very powerful species that could pose a massive threat to humanity, WY's intelligence spooks want to keep their own hand hidden until it is forced into play. I'm sure that they're afraid that humans could get themselves into a lot of trouble if they attempted to pursue "first contact" with a hostile species. As that log in the final Alien level shows, people such as "Dr. Chris Lund" would like to believe any being more advanced than us is clearly morally and culturally beyond us as well.
I liked this element of denial in AvP2. Its very fitting of Weyland Yutani. Apparently, Xenomorphs are now known to at least the Colonial Marines, so they couldn't quite keep the lid on that one. Predators, however, are a different story. I would love to see Corporal Harrison's debriefing with the board of review for "The Incident". Having seen and killed a Predator on LV-1201, he must have been very frustrated to have the suits come up with reasons for why he must have been making it up. Very reminiscent of Ripley's interrogation in the beginning of Aliens.