Did Dev realize that Sai Baba had visited him in the form of the Sanyasi and his friends?

No, Dev did not realize that Sai Baba had visited him. The narrative in Chapter 40 makes it clear that even after serving the three uninvited guests in person, Dev's mind was clouded by a "veil of Maya." It did not occur to him that the Sanyasi could be Baba. His mind was fixed on the simple idea that he was merely a guest who had come for a meal. The text explicitly states that doubt remained in Dev's mind, and this uncertainty was so strong that he later wrote to Jog seeking testimony or proof about the event, completely unaware of the true nature of his visitors.