To reproduce:
Add a RadSpinEditor and set its Hexadecimal property to true. Set its maximum to 0xFFFFFFFF(4294967295). Try to enter value larger than 7FFFFFFF(Int.MaxValue). You will notice that the value cannot be set.

Workaround:
public class MySpinEditor : RadSpinEditor
        {
            public new MySpinElement SpinElement
            {
                get
                {
                    return base.SpinElement as MySpinElement;
                }
                private set
                {
                    typeof(RadSpinEditor).GetField("spinElement", BindingFlags.Instance |  BindingFlags.NonPublic).SetValue(this, value);
                }
            }

            protected override void CreateChildItems(RadElement parent)
            {
                this.SpinElement = new MySpinElement();
                this.SpinElement.RightToLeft = this.RightToLeft == System.Windows.Forms.RightToLeft.Yes;
                this.RootElement.Children.Add(this.SpinElement);

                this.SpinElement.ValueChanging += SpinElement_ValueChanging;
                this.SpinElement.ValueChanged += SpinElement_ValueChanged;
                this.SpinElement.TextChanging += SpinElement_TextChanging;

                this.SpinElement.KeyDown += SpinElement_KeyDown;
                this.SpinElement.KeyPress += SpinElement_KeyPress;
                this.SpinElement.KeyUp += SpinElement_KeyUp;
            }

            void SpinElement_KeyUp(object sender, KeyEventArgs e)
            {
                this.CallBaseOnKeyUp(e);
            }

            void SpinElement_KeyPress(object sender, KeyPressEventArgs e)
            {
                this.CallBaseOnKeyPress(e);
            }

            void SpinElement_KeyDown(object sender, KeyEventArgs e)
            {
                this.CallBaseOnKeyDown(e);
            }

            void SpinElement_TextChanging(object sender, TextChangingEventArgs e)
            {
                this.OnTextChanged(e);
            }

            void SpinElement_ValueChanged(object sender, EventArgs e)
            {
                this.OnValueChanged(e);
            }

            void SpinElement_ValueChanging(object sender, ValueChangingEventArgs e)
            {
                this.OnValueChanging(e);
            }


        }

public class MySpinElement : RadSpinElement
{
    protected override decimal GetValueFromText()
    {
        try
        {
            if (!string.IsNullOrEmpty(this.Text) && ((this.Text.Length != 1) || (this.Text != "-")))
            {
                decimal resultValue = 0m;

                if (this.Hexadecimal)
                {
                    resultValue = this.Constrain(Convert.ToDecimal(Convert.ToInt64(this.Text, 16)));
                }
                else
                {
                    resultValue = this.Constrain(decimal.Parse(this.Text, CultureInfo.CurrentCulture));
                }

                return resultValue;
            }
            else
            {
                return this.internalValue;
            }
        }
        catch
        {
            return this.internalValue;
        }
    }

    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(RadSpinElement);
        }
    }
}