If I understand everything correctly, it seems that using opam and wanting to link to freebsd libraries installed by pkg needs the pkg-config utility which is in devel/pkgconf. Thus this is a suggestion to add devel/pkgconf to the RUN_DEPENDS list. This will help people less skilled than I am unravel the cryptic error messages that follow from -not- installing devel/pkgconf. :)
Is this still an issue?
(devel/ocaml-opam maintainer here) thanks for your report. opam itself does _not_ use pkgconf, but some packages which are in opam-repository use pkgconf -- this is handled by opam-depext (which calls out to the OS package manager to request installations of these dependencies). there's no need to include pkgconf as RUN_DEPENDS for ocaml-opam.
Rejected by maintainer per comment #2.