If this style does not meet your personal requirements, you need to edit its template and change it in the way you need. In RadGridView there are four elements which represent indentation of their parent elements:
GridViewIndentCell - represents the Indent of a GridViewRow GridViewHeaderIndentCell - represents the indent of GridViewHeaderRow GridViewGroupFooterIndentCell - represents the indent of GridViewGroupFooterRow GridViewFooterIndentCell - represents the indent of the GridViewFooterRow
Within the templates of GridViewRow, GridViewHeaderRow, GridViewGroupFooterRow and GridViewFooterRow they are represented by the following part, which is called PART_IndentPresenter. You can read more about this in our online documentation, please follow this link.
If you need any further assistance, please let me know.