I could not get an internal uniqueness constrait from the toolbox (....) to apply to a role or set of roles in a FactType. Selecting the IUC from toolbox allows it to be brought over to the work area, but a do not enter icon appears when it's over a role (as if it doesn't enter or prematurly leaves edit mode). It can't be left in a none role place on the workspace either, and can't be commited to a role by clicking or ddbl clicking.
Adding ICUs by rt clicking on a role (or shift for adding roles), works as expected.
This is the 12-2006 TCP installed on VS 2005 SP1 BRN..