We just got back from Aulani and charged everything to the room. It posted to our Capital One Venture card as a lump sum, and we were able to redeem our rewards towards that total. Our rewards also have to be applied to a travel category.
The limit is internal. You don't have to keep checking on it. If you're at a value for example, once you hit $500, the desk will automatically post the charges to your credit card. It then resets and they will post it again when you reach another $500, and so on. You don't have to ask them to post it, it happens automatically and you can keep charging to the room throughout.