Well I'm a muslim ... but i still eat pork-chops in-game, because it's a game, it's not real. Islam tells us that we can only defend ourselves, not attack - but I still play war games because again, it's not real.
Personally I think it all depends on how strongly someone feels about something. For example, if someone is vegeterian and isn't totally obsessed with that fact, they'll probably still "eat meat" in a game, but if they're totally obsessed with being vegeterian, then they will probably survive on any non-meat food.
At the end of the day, it's all a matter of psychology