I've met a few devs from Jane Street - very nice people. Had the pleasure of meeting Yaron Minsky as well (he was a guest lecturer). Harvard had an entire intro course dedicated to OCaml...while it was a nice introduction to functional programming I can't say I've ever touched the language since...
The first and the only.
What about Ahrefs? Also, some people must be using Ocaml's cousin F#, or Jon Harrop would not have a job.
Edit: oh, finance. Right.
Last time I've checked, Harrop was everything but happy with the current F# situation (tooling, ecosystem, etc.)