One way is A-OK.
When you make your DME reservation, just tell them you need it one-way and which direction that will be.
Actually, if you only need it from the resort back to the airport, it'll be a lot easier for you to just make the reservation when you arrive at your resort. Unlike the ride from MCO to the resort (which needs advance reservations and some paperwork), the ride from your resort to MCO requires only a 1 or 2 day advance reservation, and you most certainly can do it right there at your resort.
If you make the reservation in advance from home, it'll complicate matters because you'll be sent an entire DME packet, which will include bus vouchers to use from MCO to your resort, plus DME luggage tags. This will be confusing because you'll need neither on the way from resort to MCO.
So take my advice, just wait 'til you get to your resort to make your DME reservation ... just don't forget to do it!!!