The binary is installed to /usr/bin/vault, but the service (/etc/init.d/vault) tries to start "/usr/sbin/${SVCNAME}". Probably, changing sbin to bin in the service file will fix it.
Thanks, this is fixed in git: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=ca33af0c07b165bd5d81f73662fff714e3e1c48a