> Mind naming any fundamentally new concepts introduced by Haskell or OCaml?

For OCaml:

- row polymorphism (in particular polymorphic variants)

- higher-order and applicative functors (not the Haskell thing).

- first-class modules

For both:

- Higher-rank polymorphism

For Haskell (and now in both):

- GADTs

By introduced here, I'm ignoring them being implemented in toy languages first (since that is simply the first step of introducing them to programming). Similarly, it is not reasonable to say that F-omega or a dependently typed calculus already had such features, because that ignores issues of type inference and efficient implementation.