In the "Operations" part of the company it appears you're right, "most work is in Python": http://www.itasoftware.com/careers/jlisting.html?uid=718167
In "Engineering", Lisp tops the "particularly valuable" list at the bottom of "Knowledge and Skills" for http://www.itasoftware.com/careers/jlisting.html?uid=730130
Farther down the same page they ask you to solve puzzles. "Puzzles submitted in C++, Lisp, Python, Java or Perl will be reviewed most promptly, because those are the languages we use every day"