Anecdata incoming: a company I worked for had such a referral. They bombed the interview. The referring employee was incredulous. I was asked to re-interview them. They did seem good, they got an offer. The experience delayed things, put a bad taste in the candidates mouth, they took a different offer.
My point, the result of interviewing a good developer is potentially random. There is perhaps less probability of a bad developer having a random outcome as well, but certainly can happen.
Though.. define "good". Some people are incredible only when in the right team and environment.
Expert on X: "I know a little about Y, but not too much. I mostly use X for my work; I could show you how to solve the problem using X."
Interviewer: "Thank you for your time; goodbye."
When I tried to figure out why this happens, the answers are usually something stupid like: "HR posted the job announcement, they have no idea what we really need", or "yeah, we are still looking for an expert on X, but we need an expert on Y more urgently". (The latter still does not explain why they rejected the expert on X without asking him anything about X, but to the person who said this it seemed to make perfect sense.)
My point, the result of interviewing a good developer is potentially random. There is perhaps less probability of a bad developer having a random outcome as well, but certainly can happen.
Though.. define "good". Some people are incredible only when in the right team and environment.