To be completely honest, yes, in my opinion, that would be tacky. Dreams is a high-end beach restaurant. They have everything you could possibly want, and give you fabulous beach chairs and umbrellas free in consideration of your dining and drinking at their restaurant. I can't imagine why you would even want to bring a cooler there, unless you have a medical condition that requires medication that must be kept cold. In that case, I'd point it out to them when I arrived so that they would understand why you have a cooler. Otherwise, it's like taking your Big Gulp into a fine dining establishment. Again, just my opinion.