Yes. I believe "unity in diversity" is an appropriate term to describe India.
Diversity: India is a large country and people of different parts follow different faiths, speak various languages, eat and wear differently. This shows that India has a diversity spread across its people.
Unity: Despite the diversities, as Indians, we are one. As Indian, we are no more a Gujarati or a Bengali, we celebrate the national days with equal zeal, we sing the national anthem with the same passion. This shows our unity. Therefore, the phrase "unity in diversity" is justified.
Nehru has written in his book "The Discovery of India", It was something deeper and within its fold, the widest tolerance of belief and custom was practiced and every variety acknowledged and even encouraged." He means that when one ponders over it deeply, one finds that India is not only united, but its people also know how to accept other customs and beliefs.