Oculus supports South Korea so Quests bought from the Oculus Store and shipped directly to South Korea include free delivery, Oculus warranty and the 30 day return period so RMA's should definitely be covered.
With Amazon, it's a little different as there can be multiple sellers and not necessarily official partners so you need to make sure it says 'ships by and sold by amazon.com'.
It looks like Amazon only have the 256GB version for delivery to South Korea so if your were to buy the 64GB versions from the US store and have a third party ship it to Korea, that could be a problem when getting Oculus support as the delivery address as far as Oculus are concerned would be the delivery company and not your address.
Buying the 256GB with 'ships by and sold by amazon.com' stated, should be ok. I'd welcome confirmation from other Korean forum members though!