Well.....speaking from my own experiences here and I know RTR will totally disagree with me. I have found Dwarf Puffers not to be too aggresive. I have my 2 Dwarf Puffers in with my South American tank. Cardinal Tetras, Glass Catfish, German Rams, Ottos, Shrimp, Rummynose Tetras and Red Minor Tetras. I have had them in there for about 5 months now and the only issues I had were with my Corys. I have since moved them(the corys) to my 10 gallon tank....but other than that no compatibility issues whats so ever. I even had my 2 Cichlids in there for a while(Lelupi and Masked Juile) with no issues at all. The reccomended approach is for a species specific tank to be safe I suppose, but then again you could say that about most semi-aggressive fish.
It seems that any slow moving fish with fins....Beta,Guppies, Corys are going to have a rough time with DPs, but fast moving Tetra schoals or other semi agressive fish seem to do ok. Again...im speaking from my own experiences here.