I am not 100% sure of this, so check it out to keep me honest, but since the renaming of Walter Reed Hospital, i think this program has been changed over to a different address and is running thru the Red Cross. The address i got for this program is now:
Holiday Mail for Heroes
P.O. Box 5456
Capitol Heights, Md 20791-5456

As stated before, double check me on this, but there would be nothing worse then sending Christmas cards, meant with such great thoughts to a dead letter box. Also their suggestions are:
-use a generic salutation, such as "Dear Service Member".
-personally sign each card sent.
-do not include personal email , home address, photos, or other inserts.
- & avoid sending cards with glitter (could be harmful to the health of the recovering soldier).
I hope this helps, another idea is to bundle several cards in one package, make 10 recovering soldiers happy instead of just 1. Bring a smile to a recovering soldier, we owe them so much. bob.