If it brought all the actors together, then it is party to the collusion.
However, any damages levied on Apple will likely just be fines, probably in the low single millions range. They probably won't fight this too hard. To them, the worse that happens is they have to drop the agency model.
The publishers, on the other hand, may end up paying out the wazoo.
Apple brought them together to offer them better deal. Last time I checked negotiating by itself is not a crime. Apple gains nothing by increasing eBook pricing. In fact, when Apple announced iBookstore everyone thought it will fail because the prices are higher than what Amazon.
This lawsuit and DoJ investigation is going nowhere. It seems all what Apple is guilty of is offering publishers an alternative.