Nitin comes from the Sanskrit Root called as Nitya. Nitya means the "order". Or "regulated ness". In the Vishnu Sahasranaama (1000 devine names of Lord Vishnu Nitya is the name of the Vishnu. Nityaaya Namaha Anityaaya namaha. Meaning Order and dis order is nothing but Vishnu. The darshanaas the Laws of Vedas speak about the Cosmos as Nitya as it follows a regulated mode of expression and evolution.
Nitin means that exists in the regulated Order. The energy aspect of the Lord which is called his maya or sakthi is the one that exists in the Lord and his creation. So Nitin is the Energy aspect of the Lord and is popular among the Vaishnavites to keep this name. Vaishnavism is not a trait that belongs to the Caste but to the mode of worship relating to Vishnu.