If I recall correctly I think at some point Ocaml required a paid developer licence to be obtained from Inria. Has this changed or am I just misinformed?
Not that I'm aware of. AFAIK anyone can submit a patch to OCaml without any hurdles. There is a Consortium that companies can join and they benefit from a different licence. That might be what you're thinking of.
https://github.com/ocamllabs/compiler-hacking/wiki