Yes you can pass the Membership UserID as an update parameter to the Stored Procedure once the UserID is bound to the Grid. You may set the UserID as Gridcolumn and hide the column if you don't want to show it in the Grid using the Display/Visible property.
My selection also called using stored procedures, how do I 'add' the user id column to the radgrid. Maybe can help to provide a definition on the column? appreciate your reply.