We didn't go to Disney last year, but we went out west to visit family and left Christmas Eve. DD was really worried about Santa finding us, but somehow, our Elf on the Shelf smuggled in with our luggage and appeared once we got to my in-laws. Then DD KNEW she would tell Santa where we were.
You could also write a letter to Santa from the kids saying they will be at Disney. Or, if the trip is a surprise, have a note from Santa saying "Enjoy your visit with Mickey Mouse" or the like.
In terms of access, the first to places we lived with oldest DD had no fireplace, so my mother-in-law bought us a 'Santa Key' (tons to choose from online). On Christmas Eve, you set it outside your front door, and it let's Santa get into your house without a chimney... then, Christmas morning, the key is hanging on the tree! Even with our fireplace, DD insists on leaving the key out for Santa "just in case"... you could do the same for your resort room and Santa can come in that way.