Though the phrase "financial hub" is much more widespread (according to a Google search), I have seen "finance hub" as well on news sites. Does the second have a different meaning?
The first uses the adjective financial as an adjective (as one would expect, I suppose).
The second uses the noun finance as an adjective.
You're allowed to use nouns in this way, but it is not as commonly done in cases where there is a well-known simple adjective, so we would expect the first to be more common, and it would probably be the better to go for, if you are choosing between using the two.
That said, business-y types seem to have a particular fondness for noun adjuncts. I think they've got the impression that they're more punchy or something. (If so, they are, IMO, wrong, but there's no accounting for taste).
Finance is noun ,say like mother tongue.financial is adjective for hub,so here hub is financial and there is a finance hub .we can also say financial finance hub.so here hub is financial ,it may not be financial or we may discuss about the financial growth of the hub over given years and so on .now by saying finance hub we get similar sense like defence hub,shopping hub ,teaching hub and vice versa and finance hub is one type similar to them.