Did Sai Baba actually attend B.V. Dev's Udyapan ceremony after promising he would?

Yes, Sai Baba did attend the Udyapan ceremony, although not in the physical form that B.V. Dev expected. As recounted in Chapter 40, Baba promised he would come with two others. On the day of the feast, a Sanyasi accompanied by two other men arrived, was served a meal, and then left. Dev was initially very disappointed, believing Baba had broken his promise. However, Baba later clarified through Mr. Jog that he had indeed been present in the guise of that Sanyasi, thereby fulfilling his word exactly as he had given it.