I have noticed that we get more 'directional' questions (where is the bathroom, how to I log on to a computer, etc. etc.) when I am on the desk compared to when only librarians are on the desk. This could be because I am better at logging them or it could be because patrons are more willing to ask me those questions. I think that it might be the latter, but not because of anything about me personally. Rather, it might be just a matter of denmographics. I am substantially younger than most of my colleagues, and I get the impression that people care less about sounding stupid in front of me--"just a kid"--than sounding stupid in front of a middle-aged librarian.
It's a given that some questions in a library are going to go unanswered because they go unasked, no matter what you do. But in theory, if the library could reduce the number of questions that go unasked by hiring staff who are more approachable not because of training or attitude but simply because of how they look, would that be ethical?