Blend 1/2 cup Italian dressing, lime juice and tequila in measuring cup. Pour tequila mixture over shrimp in large, resealable plastic bag; turn to coat. Close bag and marinate shrimp 20 minutes.
Remove shrimp from marinade, discarding marinade. Alternately thread shrimp, onion and limes on 8 skewers*. Grill or broil shrimp, turning occasionally and brushing with remaining 1/4 cup Dressing, 5 minutes or until shrimp turn pink. Serve, if desired, with Mojito Mayo Dip.