I've got a South American puffer in a mixed community tank. He's been there about 4 months now, and so far has been generally well behaved. However, he has nipped fins occasionally, if the mysterious bite marks in the tails of white cheeked gobies (Rhinogobius duospilus) and platies are anything to go by.
On the other hand, the Awaous gobies, halfbeaks, and glassfish have never shown any sign of having been harassed by the puffer. That may be because these fish are smarter and/or faster than the platies. The white cheeked gobies have a habit of perching on bogwood and plants that I think makes them easy targets, and they're also rather poor swimmers, which can't help.
There seems to be a lot of variation in pufferfish behaviour even at the best of times, and what works for me might not work for you. Moreover, just because a puffer is peaceful now isn't a guarantee that it will be two years from now.
I've watched puffers in the wild, and one thing that strikes you is that they are intensely curious animals. They swim up and down plants, rocks, and harbour walls looking for food. I'm sure part of the problem with pufferfish aggression is boredom: we're not surprised when a bored dog chews on the furniture, and I think it is bored puffers that become nippy puffers. My hypothesis is in a tank with plenty of (fast moving) fish, lots of plants and rocks, sand to dig in, and snails to hunt, you maximise your chances of having a peaceful puffer.
Cheers,
Neale