Well, Jane Street Capital uses OCaml. According to "Caml trading"[1], hiring got easier when using OCaml:
"Personnel is one area in which OCaml has been an unmitigated success for us. Most importantly, using OCaml helps us find, hire, and retain great programmers."
I think we need to compare apples to apples here: other competing hedge funds may have to pay a lot more to have those hackers code in C++, Java, or (gasp) VBA.
... to a workforce that can jump ship to a competing firm for a similar package at any time. Retention is a strategic advantage in any industry where the "means of production" are between your employees ears.
"Personnel is one area in which OCaml has been an unmitigated success for us. Most importantly, using OCaml helps us find, hire, and retain great programmers."
1: http://www.janestreet.com/minsky_weeks-jfp_18.pdf