In the approach you have provided you are setting only the CellEditTemplate, which is applied when the cell is in edit mode. You can try setting the GridViewDataColumn.CellTemplate instead. Furthermore, it seems like you are trying to directly set a font in a DataTemplate. Instead, you need to apply the font to a certain element like TextBlock, as shown in the provided article.
Telerik by Progress
Do you need help with upgrading your AJAX, WPF or WinForms project? Check the Telerik API Analyzer and share your thoughts.