The Disney Mom's Panel answered my question about this and here is their answer: "You have asked an excellent question! Yes, you are welcome to rent
Electric Conveyance Vehicles (
ECV) at the location near the
Epcot park entrance and return it to the International Gateway location.
ECVs must remain in the theme park where rented and returned before park closing to receive the security deposit refund. I also want to note that after speaking to a Cast Member about
ECV rental specifics, she pointed out that the International Gateway site only has manual folding wheelchairs available for rentals. Therefore, if you plan to leave Epcot and return later in the day, it is likely that you may need to go back to the Epcot entrance location to pick up another ECV."