I've got a UK Galaxy Tab.
There are three parts to the Galaxy Tab charger: there's the cable which doubles as a USB data cable but has a custom connector into the Tab, there's the power adapter itself which is the same for every country, and there's a country specific plug which clicks into the main charger.
There will be no problem using a US charger in a European socket provided you either use a US to European adaptor, it will handle the different voltage automatically. If you want to do it long term it must be possible to get replacement plugs to fit on the adaptor.
Alternatively any generic USB charger should work (though with some phones these charge slower if they aren't recognised): I'll try to check my Tab with a generic charger and see if it notices the difference.
I don't know about the US models, but so far as I can tell none of the Tabs sold in the UK are SIM locked. Best to check though as I expect the US phone providers will do things differently.
Edit: I just did some checking. The Tab won't charge when plugged into a USB port on a computer, and it also won't charge when plugged into a generic USB charger. So rather nastily it looks like it only charges on the supplied charger.