If you implement your custom filter row using the logic for custom editors and technics used in our Demo Application, the produced filter row will work properly for RadGridView control and its layout mechanism.
Your filter row implementations looks great on screenshot. To be sure that it is work properly, please test and verify your custom row layout and visibility with a scrollable GridView or when other data operation is applied - grouping, sorting. Also, you must test the filter cell elements when the columns is resized or its visibility state is changed to hidden.
Do not hesitate to contact us if you have further questions or issues.
the Telerik team
Q2’11 SP1 of RadControls for WinForms is available for download (see what's new); also available is the Q3'11 Roadmap for Telerik Windows Forms controls.