Laurent Mazare also was a guest in their podcast series [0]. He seems to be part of their research division, which should be the part of the company that produces their most valuable output.

[0]: https://signalsandthreads.com/python-ocaml-and-machine-learn...

If you are using a niche/weird language like OCaml having a bunch of smart people work on porting useful things seems helpfull.

this is about machine learning with Ocaml, it is very strongly related to what Janestreet does.