We had to search hard for the followers of Obad-Hai, even though they are plentiful. The island of Geliandar is home to a large group of them we heard, but alas we were not allowed to visit it.
In general we know there are Clerics of Obad-Hai, but most of them are much more like Druids or Rangers. Obad-Hai is always trying to preserve nature in any possible way, but he will not stand in the way of nature.
Many a Barbarian, Druid, Ranger or hunter follows Obad-Hai. Any person to live in close harmony with nature would be a logical person to follow Obad-Hai. He is the deity to protect nature in all its forms, both in Fauna as in Flora.
Not many a temple or shrine of Obad-Hai will be found in civilized areas. Most temples appear much more like druid groves, where not only druids, but also any other follower of Obad-Hai is welcomed.
Any divine magic user who follows Obad-Hai is not required to attend services, but he is required to spend at least four weeks a year in such a holy area, where he is supposed to tend for hurt animals, and nature in general.