Hi Jeff,

Validators in dialog should work same way as in any other template/container. I tested following and it worked as expected.

<ig:WebDialogWindow runat="server" ID="WebDialogWindow1" Height="400px" Width="470px">
<ContentPane>
 <Template>
  <asp:Button ID="Button1" runat="server" Text="Submit" Width="189px" />
  <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
  <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server"
   ErrorMessage="RequiredFieldValidator" ControlToValidate="TextBox1"></asp:RequiredFieldValidator>
 </Template>
</ContentPane>
</ig:WebDialogWindow>