I live in Europe and play on a US server, so yah. The only problem might be registering with a US address / credit card, but I -think- they changed that.. and you can always switch to a non-US credit card after the game is registered.
The realmlist.wtf file in the WoW directory is a simple text fire that refers to the login server, so it's easily enough modified. If the clients are the same, I don't see why you wouldn't be able to do it.