A very nice gesture it would be, I'm sure.
<Gets into devil's advocate mode, and dons flame-retardant suit>. However, one doesn't have to put cash in someone's hand (or the equivalent) in order to show appreciation. Whats more, IMO, the idea of cash equivalent "thank you's" *can* send the wrong message to the more impressionable among us - and that there is already far too much reliance on that sort of thing in today's society.
Go to a con and see how the players treat the guest speakers.....read the boards and see the respect that is afforded the vets....heck, the mere existence of the sim and affiliated community probably raise awareness of veterans issues to a certain extent...
edog