At our ITT when I've bought tickets for parks, etc. for other people, they've always told me that I have to be with them when they use them. It's never been a problem for us because we always were buying them for people who were going with us. Maybe it depends on the tickets...some of them actually say that they are for military and some are just regular tickets but they sell them at a better price.
I know when we lived closer to Disney and had AP's that we bought through the military, they actually said on the ticket that you had to be able to show a military ID to use the ticket - that was years ago, though, so it may have changed.