The term “prophetic musician” simply describes a musician who, operating in the spirit of prophecy, testifies of Jesus. Because prophecy is simply the testimony of Jesus, it can be coupled with many different mediums. Preachers preach the testimony of Jesus; teachers teach it. Singers sing the testimony of Jesus; painters paint it. All these mediums can prophesy about who Jesus is and edify the Church.
“[T]he testimony of Jesus is the spirit of prophecy.” (Rev. 19:10)
The Bible has some amazing accounts of prophetic musicians who cast out demons and won military battles through melodies and songs.
Young David played his harp and caused King Saul to be set free from a terrorizing spirit: "And so it was, whenever the spirit from God was upon Saul, that David would take a harp and play it with his hand. Then Saul would become refreshed and well, and the distressing spirit would depart from him.” (1 Sam. 16:23)