Total Measure - Counting with Unrelated Date Table

Ok.  I think I figured this out after a lot of trial and error.  I'm posting my own solution in hopes that it helps someone else down the road.  I started by creating a summarization table that incorporates the measure I mentioned in my first post:

Commitments by Month = 
   ADDCOLUMNS(Filter(SUMMARIZECOLUMNS(
      'COMMITMENTS'[ProjectID],
      'COMMITMENTS'[NAME],
      'COMMITMENTS'[PERSON_ID],
      'COMMITMENTS'[PROJECTS_KEY],
      'COMMITMENTS'[Active Commitment],
      'COMMITMENTS'[Fund],
      'COMMITMENTS'[ProjectStatus],
      'Date'[Year+Month],
      "Commitment Total %", '_Measures'[Commit Total %],
    ), 'COMMITMENTS'[NAME] <> BLANK()), "Count", 1)

After that, I created a new measure for formatting the total line slightly differently from the individual rows:

Commitment Total-Formatted =
IF (
    HASONEVALUE ( 'Commitments by Month'[Year+Month] ),
    SUM ( 'Commitments by Month'[Commitment Total %] ),
    FORMAT ( SUM ( 'Commitments by Month'[Commitment Total %] ), "Fixed" )
)

The summarization table was the key to getting this to work as expected.