This faith is primarily practiced by the ss'tiss, who stopped following the Church of Telgard long ago in what remains to this day the Church's greatest failure (as seen by the Brantars of the Church). Daily ceremonies are held under the desert's noon sun. This would explain the lack of racial diversity--very few races can tolerate the Sun as the ss'tiss can.
Its beliefs are greatly separated from the Church of Telgard, as they feel that the Sun and Sky are the mother and father of Telgard, and the other gods are false. This of course, puts them at odds with The Church, but because of their nomadic ways and the desert ceremonies, the Church doesn't persecute them actively. They tried once, and half their army died in the desert before even encountering the ss'tiss. Then the Church tried to send the Paladins, but the Paladins refused.
Priests of the Sun are 99 percent Ss'tiss, it is necessary for them to have skill in desert survival, and none have magic (see racial limitations of Ss'tiss). They are generally neutral and removed from the rest of Telgard, as is the Sun. When they travel from the desert, they must wear a vial of sand around their necks. If this vial breaks, the ss'tiss must remain an outcast until she has proven her strength and is deemed worthy to return. In order to be reinstated, she must show that she has received "the mark of the sun", although what constitutes this mark is not clear.
Sun worshipers frequently have a low opinion of other religions, deemed weak and soft by the hardened ss'tiss. Frequently, they encounter individuals of other races whom they consider strong, and thus would respect, but they are confused by the person's insistence in following a weak religion.
Recently, a Sun Cult has risen outside of Hasst, which is very small but may grow quickly. It is yet unknown how their beliefs differ from the Temple's or indeed whether they are allies or at odds with each other.