You'll be able to eat there as long as you don't want to eat during the party.
I usually eat there about 5:30p which gets me done about 6:30p, just in time for the party.
The letter only mentions LTT & Tony's as they are the only two open late, during the party, till about 9:30p.
The rest of the sit downs in MK close when the park closes, taking ADRs till about 6:30p.