It hooks into apt but I used /etc/portage/basrc to call it before and after installing a package:

case “$EBUILD_PHASE” in
preinst)
elog “Running etckeeper pre-install…”
/usr/bin/etckeeper pre-install
;;
postinst)
elog “Running etckeeper post-install…”
/usr/bin/etckeeper post-install
;;
esac

One could also modify /etc/etckeeper/post-install.d/50vcs-commit to include the package name etc. in the commit message while emerging:

— a/post-install.d/50vcs-commit
+++ b/post-install.d/50vcs-commit
@@ -2,5 +2,12 @@
set -e

if etckeeper unclean; then
- etckeeper commit “committing changes after $HIGHLEVEL_PACKAGE_MANAGER run”
+ case $LOWLEVEL_PACKAGE_MANAGER in
+ portage)
+ etckeeper commit “committing changes after $HIGHLEVEL_PACKAGE_MANAGER run ($CATEGORY/$P)”
+ ;;
+ *)
+ etckeeper commit “committing changes after $HIGHLEVEL_PACKAGE_MANAGER run”
+ ;;
+ esac
fi

There are probably other/better ways to accomplish this and more…

Anyways… etckeeper looks like a nice and very flexible tool to keep /etc in a repository if one wants to.