This is similar to a perennial question raised on a couple of Email lists devoted to Anglican and Catholic church music to which I subscribe, and ultimately comes down to the definition of "sacred music". In the email lists, it was found impossible to agree on a rigorous definition, but it was generally agreed that we could identify it when we heard it. One view posted there was that music which a person believed served to enhance the connection between him or herself and the Almighty was "sacred", and that the beliefs of the lyricist, translator, composer, orchestrators or performers, were of little or no consequence if the work led to a closer relationship with the Almighty. The consensus was that whether someone involved in a "sacred" composition was not Christian was similar to the production of other items used in meditation and worship. Would it matter if the pews in the church, or the furniture used in meditation at home is manufactured by a machine, a Buddhist, or a Christian?
Some famous pieces of 20th century sacred music, in fact, were composed by people who were not particularly religious. And yet, they are masterworks, included in Cathedral music lists on a regular basis, and have brought many people closer to God. Examples include the Peter Warlock ("Bethlehem Down"), and Ralph Vaughan Williams ("Mass / Communion Service in g"; "Blest is the Man"), among others.
There is another issue here, too. Both Old Testament and New Testaments contain examples of where the Almighty chose to use people who did not know they had a relationship with him as agents of his will. In my view, "Christian" music by non-Christian is an exact parallel to this.