General rule of thumb is if you don't know what an appropriate tip should be, tip the equivalent of the price of a pack of cigarettes in whatever locale you're in.
'course now days that is getting quite pricey.
But, yes, you should tip RS guy even if a gratuity is added. The added gratuity is usually shared with the kitchen staff, maids, janitors, service bartenders, operator, etc. Perhaps a bit less if they're adding 15%+, but still you should tip him. That way he won't spit in your food the next order he brings to you
