Anecdotally, hiring Haskell developers seems far easier than you’d expect. There are a lot more people out there who want to use Haskell than there are Haskell jobs. Having some training is good- you don’t want to lose out on talented people because they haven’t used Haskell before, but it’s not like everything you know goes out the window when you learn Haskell either. With some help most people should be pretty proficient in a couple of months, and you can have people learn the language in parallel with learning the codebase and business domain, so you aren’t really losing that much time in practice.