Chances are Pietrus will much more effective in Nelson's system than Dunleavy will be. Dunleavy will have to playmake and shoot far better than he ever has in order to be a major part of the team under Nelson because scoring and running are 80% or more of Nelson's style and those are both a weakness of Dunleavy right now. With Baron and Ellis able to make plays, Dunleavy will have to shoot very well and, as an added bonus, pass well when he gets the chance.
Pietrus can get very far just running with Baron and the rest and finishing on the break. If Pietrus can defend like he used to to, he'll be a major player on the team and Nelson will use him for some 30mins a game.
Expect the athletes, if there is enough playmaking from Baron and Ellis, to get alot of the court time as they are best suited to the run and gun. Players like Dunleavy and Zarko will have to shoot and pass real well and if they do, they can be even more valuable than some of the more athletic players but shooting consistently is harder than running and dunking. Players like Foyle and possibly O'bryant (even Biedrins if he fouls alot and is a major liability on offense) will surely get very little time