No, I don't believe it shows up on MDX. If you called and had it added, but you are nervous about it, you can always call back and just confirm it was logged.
ETA: As Fangorn points out below there is sort of an indirect way to see it, and I double checked on mine and it's there. We've also had it set up before and not had them send the tags (or not sent in time), and as others have said, you can still have them retrieved if you have your baggage claim ticket and provide it to the Disney Magical Express peeps at the airport on arrival.