We've shipped UPS from many of the WDW reosrts.
If you ship from a resort that has a convention center, it also has a business office when you can take your package. You fill out a form on how you want it shipped (overnight, gound etc.) and you will get a receipt.
If the resort doesn't have a convention center, the front desk will give you a form to fill out, you hand them the form and your package but you will not get a receipt. I have never had a problem, but I always feel better with a receipt.
Ed