Melt butter in a small skillet over medium heat. Add onion; cook and stir until soft and deep brown in color, about 5 minutes.
Bring a small saucepan of water to a boil. Add hot dogs; cook for 3 minutes. Drain.
Cut each hot dog into 8 rounds.
Pour nacho cheese sauce into the saucepan. Cook over low heat until cheese is heated through, 3 to 5 minutes.
Arrange pretzel crackers on a serving platter; top each with 1 hot dog round. Spoon onion over hot dogs. Drizzle cheese sauce over onion. Garnish with bacon bits.
