I've implemented such a method for header cells in iGrid.NET X RC2 and will send it to you for testing.
Should we use the same method name for column headers? Perhaps, IsColHdrPartClipped or simply IsPartClipped would be a better choice. Take into account that we also have footer cells, and theoretically one day someone may request such a method for them. Then a universal method name like IsPartClipped the developer can find in the iGCell/iGColHdr/iGFooterCell objects would be the best choice.
And can you also tell us, why do you need this method for header cells?