Venom, your argument is invalid because your team could still send you out to deal with stuff and people could conspire against you, even if you're not immune. It is a world of survival and people will do their utmost to live, even if they're apart of the military branches, whilst it's less likely in the strict order of the military it will happen due to human nature.
Non-immunity is the way for me, simply because it'd make a lot more sense realistically speaking and it'd make it more enjoyable and interesting to roleplay. Whilst immune you have the guranteed survival against a zombie brawl, as a non-immune person you hold onto your life more dearly, simply because you know that a single bite or even scratch could end your life.