In FED rules, you have to have contact of some kind to have a DPI or OPI call. The only time you do not have to have contact is when a player is face guarding. I am not sure what you mean by "playing the defender and not the ball." A defender can always "play the defender" as long as he does not contact make contact with that receiver before the ball arrives or he is making an honest attempt at the ball.
Not sure that answers your question, but I tried.
Peace