Meh, I suppose its a good idea using computer games to teach the military to use tactics and so forth; the only real problems would probably be:
a) Make them think active warfare was just a game (Only the idiots really apply) and so it de-sensitises them greatly too masacring everyone, maybe it won't even teach them tactics as that can be done through other methods; someone already must have a mind capable of understanding tactics in order to use them.
b) If they cheat in the game.
(They're in the warzone, Private Biggs runs into all the enemy)
Private Wedge: WHAT THE HELL ARE YOU DOING BIGGS?!!!!!
Private Biggs: It's okay, I've fixed it so I'm Invunerable and have infinte ammo! *BLAM!* *Thunk*