See https://discourse.phabricator-community.org/t/display-error-on-the-status-page-for-svn-repos/2443 for discussion.
The UI currently shows a misleading warning that looks like "found svnlook; can't find svnlook".
It actually means "found svnlook, but when Subversion wipes PATH before executing commit hooks, we will no longer be able to find it".