Regular tourney ballers do not get as bruised as much as you would expect if you comparatively compared the amount of time they are exposed to playing paintball with the level of bruising received by your average punter and the amount of time they spend playing.
The reasons? Well, there's a few and it has nothing to do with building up a tolerance to bruising - though a pain tolerance is probably built up.
1) Tourney ballers, particularly at higher levels of play are generaly shot with better quality of paintballs then rec customers. The paint is a lot more fragile and breaks easier, taking a lot more of the impact energy out of the shot.
2) Tourney ballers tend to get shot in the hands, forearms, guns and goggles a lot more than anywhere else. This is because these areas are the only parts of the body exposed unless someone develops a side angle or mugs the player out of a bunker. Gun and goggle shots ain't going to bruise obviously and hand and forearm shots are less likely to bruise than shots to the thighs, etc.
3) Good tourney ballers get shot less. Bonus balling and train-crash practice sessions aside of course.
4) Good tourney ballers are fitter and therefore carry less body fat.
That's about all I can think of at the minute.