The documentation seems to be incorrect. When I use this code:
<Style TargetType="{x:Type xcdg:GroupLevelIndicatorPane}">
<Setter Property="Visibility" Value="Collapsed"/>
</Style>
The grouping pane does not disappear. However, when I use this code:
<Style TargetType="xcdg:GroupByControl">
<Setter Property="Visibility" Value="Collapsed" />
</Style>
It does disappear. (This is with Xceed WPF Pro 2.0 ..)
Thanks to Diego above for saving me tons of time trying to get this to work !!