If /var/run is a symlink to /run apt-cacher-ng does not start, because /var/run/apt-cacher-ng does not yet exist. "checkpath -d -m 0755 -o ${NAME}:${NAME} ${RUNDIR}" in start() in the init script helps. Also, it complains that "WARNING: -c/--chuid is deprecated and will be removed in the future, please use -u/--user instead". Just making the suggested change in the init script seems to work. That's with openrc-0.9.8.4, amd64 stable and oldest in the tree, so the change should be pretty safe.
Thanks. Both fixed in 0.7.7.-r1.