While Old Testament figures are not widely known as saints in the Roman Catholic tradition, they are regarded as holy figures by many Eastern Christians, as well as by the Carmelite Order. There is even a prayer on the feast of the Prophet Elijah in the Carmelite liturgy for July 20.
Here is this prayer on the feast of the Prophet Elijah, which is used by many Carmelites to honor the holy prophet of the Old Testament.