Heat gas or charcoal grill. In each hot dog, make crosswise diagonal cuts 1/2 inch apart and 1/4 inch deep.
Carefully brush grill rack with vegetable oil. Place hot dogs on grill rack over medium heat. Grill uncovered 15 to 20 minutes, turning frequently and brushing occasionally with butter, until hot dogs are hot and slashes begin to open.
Remove label and top from can of chili. Add opened can of chili to grill for last 10 minutes of grilling, stirring occasionally, until hot. Serve hot dogs on buns with chili, cheese and onion.