Was it Balasaheb Deo who was told to feed a black dog to overcome his obstacles with reading the Dnyaneshwari?

No, the provided text does not state that Balasaheb Deo was told to feed a black dog. While Chapter 41 does detail Deo's obstacles with reading the Dnyaneshwari, the method he chose to deal with it was different. The passages explain that after numerous failed attempts to read the sacred text regularly, Deo became distressed. He then made a firm resolve, as mentioned in Chapter 41, that he would wait for Sai Baba to give him a direct and personal order to read the Dnyaneshwari before he would attempt it again. The narrative does not involve feeding any animals.