Actually I think there is a distinction to be made. Both Haskell and OCaml are strongly typed ML-family languages, and to some extent you'll find some overlap in community interests, trending toward the academic side. But Haskell tends to be used more for type theory research, whereas OCaml is far more popular for programming language research due to its popularity for writing compilers.

While I don't have internal insight to Jane Street, some of their talks and public information seems to support the idea that they are actually doing a lot of similar work to compiler development. They have stated that they tend to do a lot of symbolic logic and analysis, and they make it sound like they create DSLs that traders can more easily use to convey trading strategies.

So OCaml does really well at getting things done, but historically it has been within very narrow definition of the types of things to be done.