That alone gives the observation questionable merit.
I think that the clip you linked to sounds more like a stereotypical 'camp' gay man accent if male at all, which is obviously testing for a different kind of unconscious bias altogether.
It'd be like saying 'Men in pink jeans do worse in bars than women in camo dresses'.
Would the supposed biases still be there if the voices were masked to sound like say, Darth Vader? Or maybe a Dalek from Doctor Who? Would there still be the same issues with speech patterns and what not if it sounded like the interviewee was speaking in robo speak?
No, the control group for that would be men who have, as you put it, "stereotypical 'camp' gay man accent", i.e. similarly qualified men who happen to naturally sound like this.