The Raiders were probably going to cut McClain after this year due to his 2013 contract, so it's not a huge shock for them. They may be the worst team in the NFL the way they are playing right now, so what does it hurt to shake things up?
BB should have plenty of info on McClain from Saban and from guys like Hightower who played with him. There are some big questions:
1. How much was a product of the Alabama hype coming out vs. his actual skill set, and does that skill set appear to have eroded?
2. How much baggage is there with the off field issues, negative attitude, etc.?
3. Can McClain play 4-3 SAM and cover TEs, or is he strictly a 3-4 ILB?
McClain was used in more of a coverage role last year in Oakland, and he did have 14 PD. I didn't see any film of him, so I have no idea how good he was in that kind of role. But the idea of moving Hightower up to DE and having Mclain-Spikes-Mayo at LB would seem attractive as a long term option. In the short term, if he can provide the kind of depth that we lost with Dane Fletcher's injury, it might be worthwhile.
As for the waiver wire, McClain's salary issue is the main thing which may impact teams from taking a look at him.
I'm sure BB will be sniffing around a bit, though it's very low likelihood of anything happening. But I wouldn't just dump on McClain. People were too quick to overhype him, and may be too quick to trash him. The time to buy is when the market is low.