There's quite a lot of complete failure to launch tranny vtubers, you can just check the 5-20 view channels on twitch. Typically their voice is either straight up male or that horrible AGP lilt.
I can count the number of tranny vtubers on one hand, and a few of those are successful only because most of their viewers haven't realised they're trans (MakoFukusame for example). Or obkatiekat where most of his viewers are just chasers.
Even if they don't know what the woman behind the screen looks like, most vtuber enjoyers at least want to be secure in the notion that they are a true and honest woman.