Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain bacon slices on paper towels and crumble.
Stir broccoli, cauliflower, Cheddar cheese, and onion together in a large bowl.
Whisk creamy salad dressing, sugar, and vinegar together in a separate bowl until sugar is dissolved; pour over broccoli mixture and toss to coat. Refrigerate salad for at least 30 minutes. Stir crumbled bacon into salad just before serving.