Overriding open-basedir seems impossible
Can't change the php open-basedir settings by using the conf.d, overrides (php and apache snippets) nor with the general server config setting (php permission).
Tried recreating webdomains (switching php-settings from php-fpm to mod-php and backwards)
Tested by using phpinfo();
Ubuntu 12.04 multiserver setup (Server 1: web, db // Server 2: dns, mail, db).