Actually, what I wanted was your second link, but I couldn't get it to work that way. I figured since this was not your average property (StyleManager.Theme), I was looking for a not so simple solution. However, it turns out the following actually works:
<Style TargetType="telerik:RadTabControl" >
<Setter Property="telerik:StyleManager.Theme" Value="Windows7"/>
<Setter Property="VerticalAlignment" Value="Stretch"/>
<Setter Property="VerticalContentAlignment" Value="Stretch"/>
</Style>
Go figure!