Place grated zucchini in colander and sprinkle with salt. Let drain 30 minutes. Rinse. Drain well. Using kitchen towel, squeeze as much water from zucchini as possible. Whisk 1 cup yogurt, 3/4 cup sour cream, 2 tablespoons olive oil and 1 tablespoon vinegar in medium bowl until well blended. Mix in zucchini, cilantro, garlic, cumin and cayenne pepper. Season mixture to taste with salt and pepper. Cover dip and refrigerate at least 2 hours to blend flavors.
