Yoga has a wide following in Kerala just like in other parts of India. Yes, there are retreats and centres that teach yoga and meditation. Apart from some of the government establishments, most of these centres are privately managed ones like the ones run by ashrams, some spiritual centres as well as those attached to resorts and hotels. And there are also trained and certified individuals who could help visitors to learn yoga and meditation.
It is always advisable to do a bit of research on the best centres on your own and take a decision accordingly.