In answer to the first part of this you can't really have polished concrete outdoors as it will get too slippery when wet.
There are other fine options though i.e. our exquisite Acid Etch will be a terrific finish or a grind and seal treatment with a non-slip sealer would work well also. To your main question, yes, like any other any solid surface, be it concrete or tiles, will absorb the heat and warm up if in direct sunlight. If you don't want any absorbed heat you could try wooden decking instead of a solid finish.