Looks like a fun deck. A few comments:
Did you try/consider Dark Confidant? Is Oath+Wraith testing better? I would almost cut the Wraith's entirely and add in 4 Confidants, but I haven't tested this.
Do you need 4 copies of Oath of Ghouls? The last list I saw that was based entirely around the card only ran 3 copies. You have the option of replacing the 4th copy with either Vamp Tutor or Demonic Consultation.
I think 3 E. Witness might be too many in a 3 color deck since she is GG. Since you have so many creatures, isn't she a tad redundant with Oath?
It lost a bit of its speed and burn options. However, the addition of Oath of Ghouls got the deck some nice lategame options.
You don't think Duress/Thoughtseize is good enough for the maindeck? That might help make up for the loss in speed and ensure you actually get to see the lategame.
I like Ingot chewer in the SB, could be nice with Oath vs. Shop decks.
With 24 creatures, another card you could look into is Thorn of Amethyst.
Good luck, the list really does look fun.
Mike