1. Sprinkle yeast over warm water in bowl; let stand 5 minutes or until foamy. Stir to dissolve yeast.
2. Mix flour, cornmeal, salt and sugar in large bowl. Whisk warm milk, buttermilk and yolks into yeast mixture. With spoon, gradually beat milk mixture into flour mixture. Cover; let stand in warm place 45 minutes or until batter is bubbly.
3. Melt butter with cumin in small microwave-safe cup on high 30 to 40 seconds, until aromatic. Beat whites in small bowl until stiff but moist peaks form; fold into cornmeal batter; fold in butter-cumin mixture.
4. Coat 12-inch skillet with cooking spray; heat over medium-high heat. Drop level tablespoons of batter onto skillet to form 1-1/2-inch circles; cook 1 minute each side, until golden. Transfer to rack. Repeat with remaining batter, recoating skillet as needed. (Can be made 2 days ahead; refrigerate wrapped in foil; reheat in foil in 350 degrees F oven 10 minutes.)
5. Place pancakes on platters. Mix sour cream and rind in bowl. Slice salmon in thin strips. Top each pancake with strip, 1 teaspoon sour cream mixture. Sprinkle with chives.