Stable sys-fs/multipath-tools-0.5.0-r1 init scripts /etc/init.d/multipath /etc/init.d/multipathd still use /sbin/runscript instead of /sbin/openrc-run.
This was fixed via https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=e5d1c56d2bb5f55ebac9f72f2b75883b084bf91f. You basically have to re-emerge the package to get the changes.