In a bowl, combine the cabbage and apples. In another bowl, whisk together the vinegar, buttermilk, mustard and sugar; season with salt and pepper. Toss with the cabbage.
In a skillet, heat the olive oil over medium-high heat. Prick the skin side of the sausages with a fork, add to the skillet and cook, turning once, until browned, about 5 minutes. Serve with the cabbage-apple slaw.