[whswhs]

I can't see anything in the setting as published that flatly contradicts this, so it certainly seems that you can do it if you want to.

What I'd be asking is, What is the artistic purpose for doing it? I can think of a few:

(1) It's the working out of the premise. The Banestorm brings together human and other beings from all kinds of places; as you suggest, it might be logical that it mixed them up. On the other hand, it does seem as if it did some sorting out, so that the Christians went to one region, the Muslims to another, the Buddhists to yet another. It might be that, for example, a minority of black people who landed in Caithness, or a minority of Koreans who landed in Al-Haz, would have (of necessity) intermarried and (probably) adopted the main local faith; their descendant might look very much like everybody else and would almost surely not have full "African" or "East Asian" features. They would be like, for example, Pushkin, who was one-eighth black African and became Russia's national poet.

(2) The theme is colonial exploitation. For that you probably want to have entirely racially distinct lands somewhere remote.

(3) The theme is cultural diversity. For that you probably want to have small populations within existing states (especially the more tolerant ones) that preserve older traditions.

(4) The theme is ethnogenesis, as in the Emberverse, where the founder of Boise as an independent state was a black American army officer with an enthusiasm for ancient Roman history. For that even a single heroic figure of the past might have founded a culture or a city—but its distinctive features need not be confined to those of their ancestral culture.