Heat gas or charcoal grill. Cut 6 (18x12-inch) sheets of heavy-duty foil. Cook rice in water as directed on package. In large bowl, mix cooked rice and remaining ingredients. Place 1/6 of mixture (dividing shrimp and scallops evenly) on center of each sheet.
Bring up 2 sides of foil over shrimp mixture so edges meet. Seal edges, making tight 1/2-inch fold; fold again, allowing space for heat circulation and expansion. Fold other sides to seal.
Place packets on grill over low heat. Cover grill; cook 12 to 15 minutes, rotating packets 1/2 turn after 6 minutes, until shrimp are pink.
To serve, cut large X across top of each packet; carefully fold back foil to allow steam to escape.