The ebuild scripts refer to /etc/cron.hourly/vnstat.cron instead of /etc/cron.hourly/vnstat
Created attachment 88050 [details, diff] patch for vnstat-1.4.ebuild
Created attachment 88051 [details, diff] patch for vnstat-1.4-r1.ebuild
Created attachment 88052 [details, diff] patch for vnstat-1.4-r2.ebuild
Fixed in CVS, thanks for reporting :)