1. Add water to a large saucepan to a depth of 1 inch; set a large vegetable steamer in pan. Add eggs to steamer. Bring water to a boil over medium-high heat. Steam eggs, covered, 16 minutes. Remove from heat. Place eggs in a large ice waterfilled bowl for 3 minutes.
2. While eggs steam, combine 1/4 cup water, vinegar, and sugar in a medium microwave-safe bowl; microwave at HIGH 2 minutes or until boiling. Stir in onion. Let stand at room temperature 15 minutes. Drain.
3. Combine yogurt, mayonnaise, mustard, Sriracha, pepper, and salt in a medium bowl, stirring well to combine.
4. Peel eggs; discard shells. Slice eggs in half lengthwise. Add 6 yolks to yogurt mixture; reserve remaining yolks for another use. Mash with a fork until very smooth. Stir in 2 tablespoons red onion. Spoon mixture into egg white halves (about 1 tablespoon in each half). Garnish egg halves with remaining red onion and chives.