There is no property to hide the caption and you cannot add tools directly to a RibbonTab, but a creation filter would easily allow you to remove the group's caption element. If you have never used creation filters before, the following article will give you a basic overview: http://help.infragistics.com/Help/NetAdvantage/NET/2008.1/CLR2.0/html/Win_Creation_Filter.html.

In your BeforeCreateChildElements implementation, return False. In your AfterCreateChildElements implementation, if the parent element passed into the method is of type RibbonGroupUIElement, iterate its ChildElements collection. Once you hit a child element of type RibbonGroupCaptionAreaUIElement, remove it from the collection and stop iterating the collection.