Netflix makes money, lots of it. But the real reason for that is not so much FreeBSD. It is the fact that at first they found a great niche (mailing DVDs to subscribers), did it very efficiently, and with a good business model. Today, Netflix is mostly a content (meaning shows) company, and they invest a lot of money into creating new shows; the distribution of that content and of the movies the license from the rest of Hollywood is no longer the dominant part of their business.
And while FreeBSD clearly has made their life easier when building their content distribution infrastructure, it was probably not vital to the effort. They could have done the same thing with other OSes, perhaps it would be a little harder, but it would have worked. I know several people who work at Netflix pretty well (their headquarters is very close by), and they are smart, nice, and hard-working.
If you are looking for companies where FreeBSD (or in general *BSD) was a vital ingredient in their success, I think NetApp would be a better example: the initial filer software was coupled tightly to FreeBSD. Alas, they are an older company, much less sexy, and their market cap is way below $100B.