They didn't say, but here's my take on it. First off, the songs will not appear in the actual movie, but on this inspired album which is seperate from the original score album. I'm guessing it's just Scott, but I think it could be entirely possible if the whole band was to get together to record some songs for the album. Right now, however, I'm just expected some new songs from Scott.
"So Save Me
Well I don't know...Know myself
And I've been on this side alone
What's beyond it?"
- "Save Me" (Alter Bridge)