AFAICS, only the pkg-clean part of gentoolkit depended on dialog; it has been replaced by eclean, which has no such interface. So there is no dependency on dialog for at least gentoolkit >=0.2.1 (I have not checked older versions).
This breaks the deptree for ~x86-fbsd right now.
I fixed it myself at this point, after triple checking (and being unable to find someone in #gentoo-dev to fix this after lots of tries).