Hello there! Yes, you can definitely use salted butter for your cake even if the recipe calls for unsalted butter.
Since salted butter contains added sodium, the main adjustment you need to make is to reduce any extra salt called for in the dry ingredients by about 1/4 teaspoon per stick of butter used. Your backyard BBQ cake will turn out completely fine as long as you make this small adjustment. Enjoy your baking and have a wonderful seasonal gathering!