Hello! I didn't really pay attention to which was the ATM on the baggage claim area. It if was a GLOBALNET ATM, those are affiliated with local bank Interbank, they are known for accepting many types of cards. However if the commission is different for you, that I don't know. There is however an ATM area with more bank ATMs on the second floor.
It is true that you don't have to fill in an immigration form, but the customs form should be filled out IF you have something to declare that goes over the "traveler's allowance", like a 2nd laptop for instance. Details here.