DME needs at least 10 days lead time to get the packet printed up and delivered to you...so, technically, you should be okay. BUT....there are times when people don't get that packet, even if they booked 6 months out!!! Mistakes happen though.
If you don't get your packet before you leave, call DME and double check that you are in their system. Then, when you get to MCO, go to the DME checkin counter, they will ask for ID and your room reservation info. They will print you up vouchers at this point for your bus ride.
Now, what to do about the luggage issue. You have two choices if your packet doesn't come. You can get your own bags at MCO and bring them to the DME bus with you. Or, you can go directly to the DME counter, give them your baggage claim receipts (they will copy them), the number of bags you checked and a description of the bags. Then they will send someone to get the bags, from baggage claim area, and they will send the bags to your resort.
Up to you which you do. If it were me?? I would get the bags myself. No way of knowing how long your bags will be going around and around at baggage claim, waiting for someone to get them and deliver them to WDW.