BBM5 will not work with this build, as it uses a 5.2 platform. No leaked builds of BBM5 will work on anything above a 5.1 platform.
And why is it that so many people just don't understand that Facebook isn't going to magically start working on a new 5.x build, the Facebook app has to be updated. RIM isn't building their OS around insignificant 3rd party apps such as Facebook, it's up to the app developers to make their app compatible with the OS. Since the OS is not supposed to be publicly available, there's no need for them to update it yet. I'm sure the update will be available when OS 5 is officially available.