Didn't used to do it.
Shouldn't do it now.
Lots of better places to put those (even a new /var/log/revdep-rebuild).
What version of app-portage/gentoolkit is that?
I am seeing it too. Must be one of the late 0.3.0 release candidates.
Actually all versions revdep-rebuild in the tree do it. It is a side effect of using /etc/init.d/functions.sh. Unfortunately, I haven't found a way to use functions.sh and tell it to turn off using syslog.
This actually appears to be "fixed" with at least sys-apps/openrc-0.9.9.3 installed as the einfo, ewarn, and eerror commands no longer are writing to syslog. Leaving open until I can verify when this was fixed.