I think that there is a significant difference between being able to survive the occasional cold snap...and expecting them to endure it every year for extended periods. Those gators have an ability to survive this unusual (and short) cold period by poking their heads up and continuing to breath, with their heads trapped in ice and literally frozen in place. It's not farfetched to think that some of them don't make it; the species survives the event, but the survivors have been likely stressed to the max.
If there is a nuclear war, humanity...i.e. some people...will likely survive. Does that mean that dropping nuclear bombs on a regular yearly basis is something that should be accepted? Extreme, of course...so let's try this instead: the area in which I live has experienced an extremely cold and snowy winter this year, even by our typical cold and snowy standards. The local deer herd is suffering badly; the animals are emaciated and weak, many have died, many more will die, and the population has taken a massive hit from the winter weather. They will bounce back, but locally the species has suffered, and the individual animals have suffered...and if we were to have several consecutive years like this, the local population might take many years to recover. It's happened before.
Suggesting that crocodilians might be kept outdoors in your area is similar; you would be exposing them to conditions that are at the extreme limit of occasional short-term survivability by some percentage of the population...but it would be every year, and for extended periods every year, not just an occasional harsh snap. You're taking the "what's the absolute smallest tank that a given species can survive in?" mentality and carrying it to an even more ridiculous extreme.
Please don't.
