The only style supported is the following:
If I use the style="SS" or style="MM" or anything at all, roo will always set the format to PredefinedFormat.DATE_SHORT in <entity>DetailsView_Roo_Gwt.java managed file. This is seems to be related to the getFormatter() method in GwtProxyProperty in the org.springframework.roo.addon.gwt.
The same problem occurs if I use style=Style.CURRENCY. There are probably many other style values that should be appropriately reflected in roo.