In a bowl whisk together the vinegar, the mustard, the creme de cassis, the lemon juice, and salt and pepper to taste. Add the oil in stream, whisking, and whisk the dressing until it is emulsified.
Remove skin from the duck. Scrape off any fat from the duck skin and bake the skin in one layer in a jelly-roll pan in a preheated 350 degree oven for 10 to 15 minutes, or until it is crisp. Transfer the cracklings to paper towels to drain, sprinkle them with salt to taste, and crumble them. Remove duck meat from the bones and chop.
On a large platter arrange the orange slices, the raspberries, and the arugula decoratively. In a bowl toss the duck meat, chopped, with 1/4 cup of the dressing, the scallion, 1/4 of the cracklings, and salt and pepper to taste and mound the salad on the platter. Drizzle the remaining dressing over the arugula and fruit and serve the remaining cracklings separately.