In a microwave-safe bowl, melt butter. Stir in the Cajun seasoning, pepper sauce, garlic powder and onion powder; set aside 1/2 cup butter mixture for serving and keep warm.
Peel and devein shrimp, leaving tails on. On four metal or soaked wooden skewers, alternately thread shrimp and scallops.
Place skewers on greased grill rack. Cook, covered, over medium heat or broil 4 in. from the heat for 3-5 minutes on each side or until shrimp turn pink and scallops are firm and opaque, basting occasionally with butter mixture. Serve with reserved butter.