Besides Annasaheb Dabholkar and Dasganu Maharaj, are any other authors of Guru biographies mentioned in the text?

Yes, the text mentions two other authors who wrote Guru biographies. Chapter 0 recalls a detailed and scholarly Guru biography written by Shri Samarth Sadguru Tembhe Swami, also known as Vasudevanand Saraswati Maharaj. However, it is noted that this work did not become as famous as the one by Shri Saraswati Gangadhar. The preface also mentions hearing about a Guru biography written by Shri Samarth Sadguru Dattatreya Maharaj of Balekundri, but it clarifies that this particular work did not seem to have been printed or published at the time.