Ok, this is a bit speculative on my part and not based on experience, and I'm hear to learn, so....
Hawaii might be just as tropical as places where tropical fish are from, but the one consideration I'd have with tropicals in this instance is water volume.
More specifically, freshwater tropicals reside in much larger bodies of water than a 60 gallon pond (rivers, lakes, rice patties), and these large bodies of water act as heat reservoirs -- heating and cooling more slowly, with more even temperatures than a 60 gallon pond.
Average lows in Hawaii in the winter are in the low 60's, and the smaller water volume will cool to somewhere in the 60's overnight -- too cold, as I understand it, for most tropicals. That's just the average. Cold spells can get significantly colder. For example, the record low for Honolulu was 42 degrees Farenheit set in July of 2004. I don't think many tropicals would survive such temperatures in a 60 gallon pond though they might in a lake which, again, cools much more slowly and remains at a much higher temperature than a 60 gallon pond would given the same ambient air temperature.
