Since "$VH_ROOT" is "/www/$VH_NAME", should not
php_admin_value error_log /www/$VH_ROOT/logs/php_errors.log
be
php_admin_value error_log $VH_ROOT/logs/php_errors.log
?
If the directory /www/www/$VH_NAME/logs/php_errors.log does not exist, the log file will not be created.
You can verify...