With something that big, they would have to be. Maybe not the leaders we know, but some of the others.
Which is good because I would hate to have to hate some of the leaders we met.
I just want it to be an extraordinary thing, rather than just a few of people from a few races meting and deciding that they can send an ark to another galaxy. It just can't be that easy to escape the reapers, so I wouldn't like something that simple.
Part of me think and/or hope that how the civilizations on the Andromeda got there won't be something said directly, that we might have to play the whole game to get that information for example. Although from a marketing standpoint, it would be difficult to avoid answering the question that most ME fans wants to know.