of course it matters! Probably moreso in a band than in anything else. We are talking about a singer, a frontperson, that (possibly) looks like a woman but (possibly) sings like a man. Of course that matters. What songs are the band gonna play, female or male vocal based? Will the singer have a man's or woman's voice? it matters, jeebus you can't play bass in a Beatles tribute band unless you are left handed, so yes, appearances matter in music
I worked with two men that trangenderred into women, with a year off work during the process. It is very hard to see them as a woman when you've worked closely with them as a man, it just IS. Different to meeting a trans person for the first time, it's much easier.