Every questionnaire I have seen asks whether parents (and sometimes siblings) were college athletes, so I think it can matter. But I don't think it's a factor that is going to get a coach to respond to an initial email--and as others note, it could be a hard thing to mention tactfully as part of an introduction. I think I'd omit it; but I also don't think it's something you should be too concerned about either way. Others may disagree, but I think metrics are the only thing most coaches see when sifting through a few hundred unsolicited messages. Later in the process communications get more personal.