I think I'm getting what you're doing...arrive at MCO, rent a car and head to Kennedy for the afternoon. Return to MCO, return the car, take DME to your WDW resort. Question is...if you tag your checked bags, will DME grab them for you in the morning and take them to your resort, while you are off at Kennedy for the day. (I think).
That shouldn't be an issue. Plenty of people let DME take their bags while they get a rental car...and they go directly to WDW. I don't think there would be any issue with you tagging your bags, letting DME grab them, and then your heading to Kennedy for the day. You will spend a fair amount of time traveling around Florida though. If you land at 11:30, you will get to Kennedy by about 1pm...takes time to get to rental counters and then out of the airport area, plus 50+ min drive to Kennedy. Then, an hour back to MCO, return the car, it is now 8ish...DME to your resort...you should be at the resort by 9:30ish.