It's just an exho, not a big deal although we all know that indoor HC is Nalbandian's strongest surface. I wouldn't be surprised if Nole simply let Nalbandian win against him. I doubt Djokovic will take match too seriously.
Btw, just curious, how much money are Nole and Rafa getting for playing this exho?
I didn't see anything about a Djokovic-Nalbandian match.
In Buenos Aires there will be another Nadal-Nalbandian and Nadal-Djokovic plus a doubles match between these 3+Monaco. I think that's all.