Really, I suppose it depends on just what the question means. If it means, Could we sing the Sanctus in Evensong, it would depend on what church you go to. If it means, Can we sing it in the shower, the answer is, Who's to forbid it? If it means, Can the threefold "Holy" be used in some other context, the answer is: Sure. Think of the Protestant hymn "Holy, holy, holy, Lord God Almighty, early in the morning . . ." We Pravoslavs have a number of troparia and stichera that quote them, for example the morning troparia the first of which is: Arising from sleep, we fall down before thee, O Good One, and the angelic hymn we sing to thee, O Mighty One: Holy, holy, holy art thou, O God; through the Theotokos, have mercy on us."

Stephen