> When invoking ocamldoc, either directly or through ocamlbuild + .odocl,
> the generated documentation only contains the name of modules, without
> any of the comments or even the values.

Usually ocamldoc works fine with submodule:

===== sub.ml
(** This is {!A}. It contains a properly-documented submodule {!A.B} and a
     single value {!A.a}. *)
module A = struct

   (** This is {!B}. It contains a single value {!B.b}. *)
   module B = struct let b = 1 end

   let a = 0

end
=====

$ ocamldoc -version
Ocamldoc 3.10.1
$ ocamldoc -html sub.ml

Hope this helps,
Julien Signoles