Sure. And most of that happens in the context of "refer anyone and we will vet them with our hiring process". If you change that to "only refer people whom you personally vouch for because we will trust your judgment to replace parts of the hiring process", there will (or can) be incentives to refer people who are really good, not just people you personally like and would like to help out. If you combine that with hiring people who've worked in diverse environments, that might counteract the natural referral biases.