To hide the orders of a channel group from the order report page results, please set the setting 'HIDE_IN_ORDER_REPORT' to YES for any one of the channel belonging to the that channel group.

For Example. To hide channel group A consisting of channels X, Y and Z.
Set the channel setting 'HIDE_IN_ORDER_REPORT' to YES for either of the channel X, Y or Z.

Note - This will only work for WH V9 site.