Are Android OS updates region specific? Well, I have a Galaxy Ace with 2.3.3, build XWKPY and Samsung Kies doesn't show an update to 2.3.4 yet.

I'm thinking of manually updating it through Odin and I need to know if I can just download any Gingerbread 2.3.4 update file or is there anything else that I need to be worried about?
Android OS updates can be region specific. It depends on the OEM builds. In case of Samsung, yes.
You can update through Odin, but other region binary may not have the required operator information or other settings related to your region.
I suggest you wait for an update in Kies. Should be available soon.