I don't think I've ever worked for a company with such a referral program (including a couple of large tech companies). Or maybe I just wasn't told about them. Although they wouldn't make any difference in terms of encouraging me to bring in new hires.

If I enjoy working at the company, then I will do that regardless (assuming I know a qualified dev who's looking for work, which is pretty rare), and if I don't enjoy working at the company, then I won't.