A counter-tenor voice is obviously an advantage for vocal parts written for that range (in relation to the accompaniment) but with lyrics suggestive of a male narrator. (Besides, there is not much non-"early" repertoire suitable for counter-tenors. Well, the "late" Bee Gees may qualify.)

Female singers make for slightly less "realism" - but then, that music is so highly artificial that it scarcely matters. Male voices singing an octave lower may cause problems, though, since that corrupts the musical architecture of many tunes with elaborate accompaniment.