Toss zucchini and 1/2 teaspoon salt in large bowl.
Let stand 5 minutes.
Transfer to sieve. Press out excess liquid; place zucchini in dry bowl.
Mix in egg, yolk, 1/2 cup flour, cheese, and 1/2 teaspoon salt.
Mix in parsley, onions, and dill. If batter is very wet, add more flour by spoonfuls.
Heat 2 tablespoons olive oil and 2 tablespoons corn oil in large skillet over medium heat. Working in batches, drop batter by rounded tablespoonfuls into skillet. Fry patties until golden, 5 minutes per side, adding more olive oil and corn oil as needed.
Transfer to paper towels. DO AHEAD Can be made 1 day ahead.
Place on baking sheet, cover, and chill. Rewarm uncovered in 350°F oven 12 minutes.