I am a Persian Gulf Veteran, was in an M1A1 Tank and I went through some rough times in the 90’s dealing with it.
World Of Tanks offends me, personally. As a whole I do not play first person shooters except in Story mode for similar reasons to what your coffee shop dezian says, but, I’m not going to go aggro on someone for making them. The entire idea of health being a resource that builds back up shortly after being shot is actually insane, energetic shields sure, but not health.
But, that doesn’t matter, the more real that it is, the more not fun it would be to play. Depending on how well a random veteran slept the previous night your just asking for some grief. I was the coffee shop Veteran for a while in the late 90’s while I was getting my s#!t together.
Games are meant to be fun, and realistic is not fun. The place for asking advice from Veterans is on details such as uniforms, equipment, slang they may have used ect., maybe what songs they listened to at the time If the guy has unresolved issues who knows what he’s thinking, or how much of what he says is true.
If it’s a place you will see him a lot it’s probably best to get him on your side. One idea is to ask him if you could give him an interview, and take notes of what he says answering your questions. Try to keep the conversation about him and away from your game. He may become someone who will watch your back at the coffee shop.