Square and other would have to pay. Koei who has been a loyal sony dev forever had to pay... so I dont see why Square wouldnt.
Because if Square say "we're going to make Final Fantasy a X360-exclusive title" lots of people will buy an X360 just for that. They might say that if, for example, Microsoft were to offer them a ten-figure sum for FF exclusivity.
Dynasty Warriors is one of those titles that will sell many units but it won't sell many consoles.