I often use Melodyne for vocal harmonies … but only for testing purpose: check out how some kind of harmony would sound and after making decisions just ditch Melodyne harmonies and sing them myself.
But when working with talented singers (that’s anyone else that myself) I try to avoid using Melodyne alltogether. If they are there behind Microphones I just try to hum them what I would like them to sing … a lot faster than dragging those blobs up and down on the computer screen.