Why "exceptionally" high? The programmers you are hiring are (or should be!) bright, they learn new things fast, and OCaml is not very difficult to learn.
At any software company you have to learn new things. Every company has its internal development stack and custom software, unless the company literally isn't a software company at all or is doing something so unoriginal and dull that you wouldn't want to work there.
At any software company you have to learn new things. Every company has its internal development stack and custom software, unless the company literally isn't a software company at all or is doing something so unoriginal and dull that you wouldn't want to work there.