I have seen them kept in marine set ups but advise against it..like all puffers they are cheeky little guys and will happily munch any snails, shrimp and even some corals !!!!!!
It's not a matter of can they, it's a matter of should they. Sure they can be kept in marine for a little bit, but they are really a brackish species. I'm not sure how that would affect their long term health if kept in those levels for long periods of time. Something for you to google, I guess. Or go ask in the brackish forum. Nmonks is over there and he'll be able to tell you. He's awesome and has written books on brackish fish