Hi Konstantin,
You can hide the table in the GGC, by having a customengine. Derive the GridChildTable in the CustomGroupingEngine and override the GetVisibleCount(), there check for the tablename you want to hide through the ParentTableDescriptor.Name and return 0.
Refer to the attached sample for more details.
Here is a sample
http://www.syncfusion.com/Support/user/uploads/GGC_HideTable_fd9f811a.zipRegards,
Rajagopal