Having worked in the quant industry outside of JS, and being good friends with a couple JS employees, I'm of the opinion that in 2025 ocaml is hurting JS more than it helps them. Using an obscure programming language absolutely can help out your hiring effort at a small company; for example, I did an internship at quite possibly the only US-based company doing Common Lisp that hired undergrad interns. All my coworkers were extremely talented because (a) people who use Common Lisp are definitely PL enthusiasts rather than your typical FAANG-oriented CS college student and (b) without anywhere else to really go for an internship, they all ended up at this company and (c) they only needed a few interns so could afford to select only those who had prior common lisp experience.

But Jane Street is big enough now that 90%+ of their software hires aren't joining /because/ of ocaml, but in spite of it. The well of existing ocaml (or more generally, functional programming) enthusiasts who are qualified and willing to work for JS has been depleted for some time now. Rather than ocaml being a sort of shibboleth to hire only engineers who are passionate about programming languages, JS now hires the same sorts of engineers who would work at any other quant fund (ie, generally smart CS students who grinded C++, python, and leetcode questions in college), offers them slightly more money and a slightly nicer office than their competitors, and sends them all through a 2-week ocaml bootcamp.

but oh well, maybe ocaml is still worth it for the 10% of hires who actually are FP enthusiasts and would have otherwise gone into academia.