I don't quite see how one is meant to determine if they've been hit or not. With paintball, it's almost a definite certainty of knowing, with pellets, there's no telling. (obviously never played it before, I believe it's banned in Aus, might be wrong)
On loose, but thick clothing, paintballs will break even when there is not contact with the human body. However, I really doubt you would feel that with a pellet. Sure on the body, but on loose clothing, I don't think it would warrant a surrender. And this is especially in the heat of battle when adrenaline is pumping.
Many times in paintball, you would get someone on the shoe. That would warrant a surrender as it would leave a mark - I don't think you'd feel a pellet on the shoe.
But other than that and a few other trivial cases, it seems genuinely interesting and fun.
I was invited to playin' paintball, But the guys i was gonna play with didn't have any protective vest or any of that crap, and i've seen before hand what paintballs does to the body. Not pretty.