Actually I think that is exactly your area of expertise! and its good to see you posting again!!
I also am inclined to agree with your assessment on this piece, especially that it is probably composite, which is of course typical of Confederate edged weapons of the Civil War, and supporting the plausibility of that suggestion. The interesting ivory (or bone) grip is naturally supportive of this. I've seen numerous swords and various edged weapons of this period which had been regulation weapons, and were refurbished with interesting grips with bone and ivory. I can recall one very nice M1840 NCO sword I had (many moons ago
) which had been mounted with a beautiful bone grip. Whether it was captured and reworked by a Confederate soldier is anyones guess, but it certainly wasn't done for continued wear by a Union NCO.
The Confederate edged weapons of the Civil War are in many, if not most cases, anomalies that are specially furbished or one off cases using the components of other weapons that become variations of certain types or forms. The huge Confederate 'bowies' are an example, and these in many instances turn out to be various incarnations of 'espada ancha' from Mexico.
The best reference I can think of that might have some lead on dirks of this general form would probably be "Boarders Away" by William Gilkerson.
All the best,
Jim