Porcupines, and other puffers in the Diodontidae family, are probably the most reef safe of the large puffers. Granted, when I say reef, I only mean corals. Their mouths(teeths) are a bit different from Arothron puffers, so they don't 'chew' on the live rock per say.
That said, any large puffer will probably go after all inverts. Small fish are a definite risk with a Porky too. What do you mean by "tankmates"? Lastly, I hope you realize the size these guys can and will reach, and the massive bioload they will put on a tank. A 55gal will not cut it for a Porky.