DECLINED: Currently, RadDock is designed to only persist the position of tool windows. The document windows are consider to be kind of dynamic content presenters which need to be opened/closed at runtime. 
ORIGINAL DESCRIPTION:
Create a single ToolWindow, set its DockState to Floating, add this window to a RadDock. Start the application, hide the window, save the layout, then load the layout, the window is not hidden. In the xml there is no node with ToolWindow

To  reproduce:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        ToolWindow newTool = new ToolWindow();
        newTool.Name = "New Tool";

        newTool.CloseAction = DockWindowCloseAction.Hide;


        this.radDock1.AddDocument(newTool);
        newTool.DockState = DockState.Floating;
        this.radDock1.ActiveWindow = newTool;
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        this.radDock1.SaveToXml(@"..\..\layout1.xml"); 
    }

    private void radButton2_Click(object sender, EventArgs e)
    {
        this.radDock1.LoadFromXml(@"..\..\layout1.xml");
    }
}