I cannot vouch for the winter, but you can put an aro or an other tropical in an outdoor pond in California from April/May - September with no worries. You will not need a heater or anything. Just a filter and some plants, and you are good to go. Trust me, your fish will love it, and they will look great after being in the sun for 5-6 months.
i've lived as far north in texas as abilene an witchita falls and as far south as houston, in both places i've seen it snow plus in texas you can never rely on the weather, there's a saying "if you dont like the weather here wait a few minutes"