no, if Fred had decided to take part in a local amateur Gilbert and Sullivan, or alternatively taken part in a rock and roll night and sang Rock around the clock , while he was singing either G and S, OR ROCK AND ROLL he would not have been a traditional singer.
a traditional singer is only a traditional singer wnen he is singning traditional material he learned orally, once he starts singing Rock and Roll or Jazz, he becomes a Rock Roll singer Jazz singer or LightOpera singer.
lets take Rev Gary Davis he is described as a blues and gospel singer, so he was only a gospel singer when he was singing gospel music, he was a blues singer when he sang blues[ he could not be a gospel singer when he was singing blues cos he wasnt singing gospel music.
so logically if FredJordan sang Rock Around the Clock , He was singing Rock and Roll, so he is a Rock and Roll singer.
he cannot be a traditional singer and a rock and roll singer at the same time