In small bowl, combine honey, ketchup, vinegar, horseradish, garlic and red pepper flakes until well blended. Reserve half of sauce and set aside.
In separate bowl, mix together remaining ingredients, except buns. Blend in 2 tablespoons of reserved sauce.
Divide salmon mixture into 4 patties, 1/2 to 3/4-in thick.
Place patties on well-oiled grill 4 to 6 inches from hot coals. Grill, turning 2 to 3 times and basting with sauce, until burgers are browned and heated through. Place on hamburger buns and serve with reserved sauce.