Standard Chartered uses their own dialect of Haskell. There's some talks on youtube about it.
I've done Haskell contract work at multiple large Wall Street investment banks. It's not like it's their only language - these are large orgs with lots of smart people, sometimes some of them use Haskell.
Jane Street uses OCaml, but of course that's not Haskell. All the other finance firms seem to use pretty standard C/C++ because they need the low latency.