I would take that study with a rather large grain of salt. The validity of such studies depends enormously on the details of how the data was gathered, and without digging into those details, I'm not sure it's much more than noise, especially because the thing being measured (functional programming jobs in industry) is quite small, and not a major part of the survey. I don't know that one should trust this any more than one does the TIOBE survey of programming language popularity.
My own experience points in the opposite direction of the data listed in the study. It seems pretty clear from our experience in the hiring market that people with OCaml in their background are in high demand, and that the places that do hire people to program in OCaml itself need to pay good money to be competitive. I know Jane Street pays quite well, and I suspect that Bloomberg and Facebook are also compensating their OCaml-wielding employees in a competitive fashion as well. Also, from what I know from the banks that hire FP types (a lot of it in Haskell), the compensation their is pretty solid as well.
y