Dressing: Whisk all ingredients to blend in a small bowl. Season dressing to taste with salt and pepper.
Salad: Steam sweet potatoes in batches until potatoes are just tender, about 10 minutes per batch. Transfer sweet potatoes to large bowl. Cool to room temperature. Add green onions, parsley, pecans, and all raisins. Pour dressing over, toss gently to blend. Season salad to taste with salt and pepper. (Can be made 2 hours ahead. The salad can remain at room temperature up to two hours before serving.)