On the newest 590 SLi i think you can... but its only the latest one, so make sure you get that. I would also reccomend getting an ATi CrossFire chipset anyways if you want to CrossFire your ATi cards.
Ya,i believe nvidia chipset mobos are only SLI,except for what Burgerbob said,which im not sure about,but usually a crossfire board will have an ati chipset i believe.