HI Meredyth,
Yes, you are right. In the past, Walt Disney World has offered a military discount on
Mickey's Not So Scary Halloween Party. The military discounts have usually been given for the parties that happen in the month of September. Official announcement of the military discounted tickets should be released once we get closer to fall.
When it comes to using military discounted tickets, whether they are for special events like Mickey's Not So Scary Halloween Party, or Disney's Armed Forces Salute theme park tickets, the military member that purchased the tickets needs to be present in order to have them validated. So, your son would have to be with you in order for you to use military discounted tickets.
I hope this answered your question, Meredyth. If you have any more questions before your vacation, feel free to ask us at any time.
Have a fantastical Disney day!