to the porterポーター means “porter,” and に marks the person receiving an action or being told to do something. In 運んでもらう, it means having the porter carry something; in 運ばせる, it means making or letting the porter carry something.
JA: ホテルに着いたら、ポーターに荷物を運んでもらいました。
EN: When I arrived at the hotel, I had the porter carry my luggage.