Hi,,the answer is yes,,,of course it depends where you live, I had a 12 inch south american (amazon, silver arowana) arowana in my bakyard japanese garden concrete small pond, say 350gallons. Arowanas are hardy but not beginners fish,,I kept the water warm around 26 degrees celcius with submersible 500 watt heaters (around 1800 watts total) the pond has a large surface area, and they don't need to be deep, Arowanas need alot of space, but not depth, becuase they swim by the surface.
Yet I did one very stupid mistake,,the arowana was with me about 1 year and a half, and I kept it with a koi. One day I put some salt on the pond to keep it clean, and for the kois health,,,a month later after coming from a vacation trip and after doing no water chanbes I added some more salt forgetting that I already added some salt before, and salt doesnt evaporate, so it accumulated and you may very well guess the results of my stupid mistake... (Arowanas are from acid amazon waters, though they can adapt to a ph of 7.7).
So if you dont count the stupid mistake I made, arowanas can thrive outdoors with the right temperature, surface space and clean water.
As of now I am not adding any fish until I expand my pond, I have 2 plecostomus, one hybred parrot fish, one large angel (over two years now in the pond!!!!) and I am expanding my pond with more space and hiding places so I can add a stingray, lung fish and other such fish.. but before i need more space.