I don't think Haskell training per se would ever work.
Haskell is beautiful because smart people find it to be a really good way to express their problems and solutions. Haskell is the way their thinking comes out. So if you're in that 3% you probably know and possibly even use Haskell already because you have that sort of train of thought. If you're in the remaining 97%, you could only do much less or barely nothing at all until you had had a long series of "aha!"s, not often even related to Haskell itself.
Instead of language training, effectively a mindset-changing smartness training is what would have to come first.
For most people Haskell is the first introduction to some concepts (lazy eval, functional purity, etc.) that makes Haskell compelling in the first place. So as Haskell looks so foreign and they do not see the benefits they will reap, they do not even start. When learning Haskell you get rewarded as you progress but you have to work a little at the beginning (same with Common Lisp, at least for me.)
At $WORK I used to show some cool stuff in another language and tell my coworkers it is built-in in Haskell (the concurrency stuff is what interested them.) I hope some of them will have a look at it in their spare time.
Another possible issue, depending on your approach, can be how to integrate with external systems. I have seen teams trying to deploy a Haskell based common library to a heterogenous production environment and it wasn't pretty.
The core Haskell module itself solved a specific problem beautifully, but it all got very messy outside the confines of the pure and pretty functional world.
Haskell is beautiful because smart people find it to be a really good way to express their problems and solutions. Haskell is the way their thinking comes out. So if you're in that 3% you probably know and possibly even use Haskell already because you have that sort of train of thought. If you're in the remaining 97%, you could only do much less or barely nothing at all until you had had a long series of "aha!"s, not often even related to Haskell itself.
Instead of language training, effectively a mindset-changing smartness training is what would have to come first.