Heat oven to 425°F. Warm the vinegar in a small saucepan over medium heat. Remove from heat, add the raisins, and let sit for 15 minutes; drain.
On a large rimmed baking sheet, toss the Brussels sprouts, oil, and 1 teaspoon each salt and pepper. Roast, stirring once, until tender and slightly golden, 25 to 30 minutes.
Meanwhile, cook the bacon in a large skillet over medium-high heat until crisp, 6 to 8 minutes. Transfer to a paper towel-lined plate; crumble. Discard all but 2 tablespoons of the drippings.
Return the skillet to medium heat. Add the onion and cook, stirring occasionally, until tender, 5 to 6 minutes. Add the Brussels sprouts, raisins, and bacon and toss to combine.