Wirelessly posted (WhiteBerry Bold 9780: Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/18.104.22.1680 Mobile Safari/534.8+)
My understanding is that RIM can access BBM messages if you have BlackBerry Internet Service, but not if you have BlackBerry Enterprise Server. For BES the owner of the server would likely have access though. I don't know if this is true, but it is what I've heard.
As for RIM cooperating with law enforcement, I don't see why they wouldn't. RIM has said that they would be cooperating with British officials on issues related to the riots.