By "several people programming in it full-time" you mean "everyone who writes code in the company (IT, developers, researchers and traders) writes code in OCaml

By "several people programming in it full-time" you mean "everyone who writes code in the company (IT, developers, researchers and traders) writes code in OCaml" right?. Yaron has said (perhaps in that video, perhaps somewhere else) that the founding partners (who were voice traders, not programmers) learned OCaml as their second programming language, after VBA. The language pervades the company.