Agree with Shoes. All WDW resort guests can (and always have been able to) use all of the inbound DME services, including luggage transfers.
It's going home where there is a difference depending on whether or not you are flying on a participating airline. All guests can use the DME bus transportation service regardless of airline. However, only guests on participating airlines can use the Resort Airline Check-in service, which allows you to check in for your flight and check your bags at the resort.
To the best of my knowledge, Frontier does not participate in DME. As a result, you will need to take your bags to the DME bus and check them at the airport.