Well Madara broke the Edo Tensei, there is no way that the man who defeated him won't be able to do it as well. I'm actually surprised Tobirama hasn't been able to do it.

I also get the feeling this might be the rehabilitation of not just Sasuke but Orochimaru too. They are both essentially the same type of character but from different generations; geniuses who went crazy due to the loss of family. Hashirama might be the father/grandfather figure both have needed to calm them down. Plus there is no way these guys won't be joining the battle now that they have sensed what is going on, which would require the agreement of Orochimaru.