Did anyone other than Annasaheb Dabholkar write biographies of Sai Baba? If so, how do they differ?

Yes, the texts mention another author, Shri Dasganu Maharaj, who was a devotee worthy of Shri Sai Baba's grace. He wrote two biographies of Baba, one in his 'Bhaktalilamrut' and another in his 'Bhaktisaramrut'. While these biographies are described in Chapter 0 as excellent and heart-touching, they are noted to be very short compared to the 'Shri Sai Satcharita'. The stories are largely the same, but a key difference is that Dasganu Maharaj included commentary on the pitiable state of the country, a topic Annasaheb Dabholkar chose not to address in his work.