RadFormDecorator styles standard controls only - comboboxes, buttons, etc. It does not style or change the skins of the other RadControls - it could only style any standard controls that they are using - for example the checkboxes of RadTreeview and RadGrid.
If you want to set a common skin to all RadControls on a given page, you should use RadSkinManager
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.