Keith Bogans can't be traded until January 15 because he was a sign-and-trade. The other players can be traded now if the deal can be structured so that their salaries are not aggregated. That restriction ends September 12.
Does that mean one-for-one trades are allowed until Sept 12?
Yes, and you can also trade multiple players to the same team provided those trades can be accomplished independently.
And I don't think it's necessarily a one for one trade necessary... like I think you can trade Humphries for X & Y, you just can't do Humphries and Brooks for Z.
But I could be mistaken on this last part.