The mouse cursor should not also change to split.

How to reproduce: set certain splitter elements to be fixed, then you would notice that they have the resizing image visible and the cursor changes to split if you hover them

Workaround: manually hide the layout element and use a custom control overriding its Cursor property
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        new RadControlSpyForm().Show();

        this.radSplitContainer1.EnableCollapsing = true;
        this.radSplitContainer1.UseSplitterButtons = true;
    }

    protected override void OnShown(EventArgs e)
    {
        base.OnShown(e);

        foreach (SplitterElement splitter in this.radSplitContainer1.Splitters)
        {
            splitter.Fixed = true;
            splitter.Layout.Visibility = ElementVisibility.Collapsed;
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        foreach (SplitterElement splitter in this.radSplitContainer1.Splitters)
        {
            splitter.Fixed = !splitter.Fixed;
            splitter.Layout.Visibility = !splitter.Fixed ? ElementVisibility.Visible : ElementVisibility.Collapsed;
        }
    }
}

public class MyRadSplitContainer : RadSplitContainer
{
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadSplitContainer).FullName;
        }
    }

    public override Cursor Cursor
    {
        get
        {
            return base.Cursor;
        }
        set
        {
            SplitterElement splitter = this.GetSplitterElementAtPoint(this.PointToClient(Cursor.Position));
            if (!(splitter != null && splitter.Fixed))
            {
                base.Cursor = value;
            }
        }
    }
}