Setting GridLinesVisibility would not affect these borders because they are part of GridViewGroupRow and GridViewIndentCell. If you want to permanently remove these borders you should predefine the templates of GridViewGroupRow and GridViewIndentCell against Metro theme. I am attaching you sample application which demonstrates how this can be achieved. However if you set Metro theme either to RadGridView or at an application level the Border from the GridViewIndentCell would not disappear because we have an issue related to the style of this element in a theme different than the default one.
the Telerik team
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