Rex,
MITRE involve introduces a new wrinkle. They have a long track record on registry work - and are currently working with Google in an open source initiative - that they show cased in the recent open house at MITRE in June - for resolving enterprise information model alignment - read DoD - who have huge systemic issues (and budget $!).
Having said that - FYI - the CAM tool autogenerates a EDXL dictionary for you from the HAVE schema, and that EDXL-dictionary ships in the dictionary folder of the CAM toolkit - so that anyone can review that example.
I see this as the way forward - having shared entities such as gml: in the NIEM dictionary along with em: entities of wide applicability - but then having separate domain dictionaries also. Being able to quickly and consistently generate these is key - because cost of adoption is otherwise an inhibitor.
Notice also - that this takes NIEM into uncharted waters in that now the emphasis is potentially on the dictionary as the central means to reuse and build - instead of XSD schema... but then that's another whole religious deal to take on board.
Thanks, DW