There is no solution to hide the indent cell for the version that you are currently using (Q1 2008 SP1). Your requirement, however, could be implemented easily in the latest Q3 2010 SP1 version. Feel free to write back if you need assistance regarding the latest version.
the Telerik team
Q3’10 SP1 of RadControls for WinForms is available for download
; also available is the Q1'11 Roadmap
for Telerik Windows Forms controls.