I am not sure why a PLIST exists for pkg_install since it has
NO_PKG_REGISTER=       # defined
NO_PACKAGE=            Deinstallation is not permitted

(Anyways, I want it to register and be able to make a package, but that is
another discussion.)

The PLIST is wrong; it hard-codes "share/man"

/bin/ls: /usr/share/man/cat1/pkg_add.0: No such file or directory
/bin/ls: /usr/share/man/cat1/pkg_admin.0: No such file or directory
...
pkg_create: can't stat `/usr/share/man/man1/pkg_info.1'
pkg_create: can't stat `/usr/share/man/man1/pkg_view.1'

With an older PLIST, I was using:

.if ${OPSYS} == "NetBSD" && ${PREFIX} == "/usr"
CONFIGURE_ARGS+=        --mandir=${PREFIX}/share/man
MANDIR=                 share/
.else
CONFIGURE_ARGS+=        --mandir=${PREFIX}/man
MANDIR=
.endif
PLIST_SUBST+=           MANDIR=${MANDIR}

and had MANDIR used in my PLIST.

   Jeremy C. Reed
   http://www.reedmedia.net/