I'm a little confused but are you using a parimutuel pool to determine payouts similar to horse racing? I've never seen this type of betting for the NBA playoffs.
Yep. All bets go into a huge pool and then divided amongst all the winners. It great for people backing outsiders as the price is often bigger and when enough people play, the favourites match the odds of backing them normally. As you mentioned this is used in Horse Racing and is a very popular way to bet.