Unroll crescent rolls and lay flat on a work surface. Cut sweet potato patties in half. Roll 1 half-patty in a crescent roll, stretching dough to cover patty completely and make a dumpling. Repeat with remaining patties and rolls.
Place walnuts in a plate. Dip dumplings into nuts, pressing down to coat the top. Place coated dumplings in a 9x12-inch glass baking dish, nut-side up.
Preheat the oven to 325 degrees F (165 degrees C).
Combine water, sugar, margarine, cinnamon, and nutmeg in a heavy saucepan. Cook over medium-low heat just until sugar and margarine are dissolved, 3 to 5 minutes. Pour sauce over dumplings in the baking dish.
Bake in the preheated oven until bubbling, 20 to 25 minutes.