I agree that it is possible for a dog to win a fight against an alligator in the dark. Anything is possible. Why wouldn't it be possible? If an alligator can win against a dog, a dog can win against an alligator. I have seen videos of even cats scaring off alligators.
Alligators are strong and fast and are known for their incredible jaw strength, but a dog's superior sense of smell would make it difficult for the alligator to sneak up on the dog long enough to clamp it in its jaw. Additionally, dogs are agile, speedy, and possess keen hearing. An alligator wouldn't stand a chance against a dog in the dark.
There are 1 or 2 breeds that are quite tough and, with a stroke of luck, may somehow win - just - but it's highly unlikely. Alligators are most active at night, and have insane reflexes and are lightning fast. A dog simply can't move fast enough or react quick enough to beat the alligator, and that's not even taking into account it's thick hide and vice like bite.
In his home environment, the alligator is formidable. He's well adapted to marshy and wet ground. He moves quickly, faster than most folks realize, if not for long distances. His jaws have evolved to clamp down and, while he doesn't always take a bite out of his prey, he easily carries the victim back into the water for drowning. The alligator is low to the ground, difficult to grab a leg or reach the soft belly, unlike most dogs. As mammals, developed to hunt on land, dogs would be vulnerable to attack by an alligator.
No, a dog cannot possibly win a fight against an alligator in the dark. Alligators are most active at night, which is when they prefer to hunt. They are very fast and agile, and their tough hide is difficult for dogs to penetrate with their teeth. Alligators would have the upper hand in fights with dogs at night.