Even better, are there any other trading firms using functional languages?
Also, if you want to consider Scala: http://quant.stackexchange.com/questions/298/is-scala-used-i...
Tsuru Capital do FP and have advertised jobs on the haskell-cafe mailing list before.
I run technology there.
Feel free to fire me off an email if you'd like to know more.
There are a number of banks mentioned such as Bank of America, Barclays Capital and Cedit Suisse. A company called Allston Trading is apparently using Haskell to do some HFT too.
EDIT: fixed spelling.