Who were the original priests of the Palani Murugan Temple before Telugu Brahmins took over?

 There are various theories surrounding Palani Murugan Temple. I describe the history and leave it to your imagination.

The idol was found by a local king (Chera) during 2nd century. Before that there is no evidence that it was worshipped by mass or a Siddha (Bogar).

It is in 2nd century, the idol was worshipped by the local king and the priests from Vada Desam (Vada Desam refers to Chozha Desam (?))were appointed by Chera. They were called Gurukkal.

4th till 10th century, neighbouring Kongu regions were ruled by Gangas, who were Jains and political uncertainty existed in Palani. Overlords of Gangas are Telugu speaking Pallavas. Tamil Siddhas did not reveal their religious identity during that time, otherwise execution. Bogar and his disciples?

(Note: Chozhas ended the Ganga rule in 10th century. Prior to 10th century, Nayanmars and Azhwars never travelled Kongu region and there are no Divyadesams. During Chozha regime, Ramanujar travelled and established Sri Vaishnavism- Karamadai temple)

Chozhas granted heriditerary appointment to Gurukkals during that time. These Gurukkals are from Chozha Desa Vadammas.

During 13th Century, Chozhas were uprooted by Pandyas for ever.

Followed was the regime of Sultans at Madurai in 14th century.

Fearing execution by Muslims, conservative Brahmins of Chozha and Pandya countries migrated to Palakkad.- Palakkad Ayyars.

Sultan rule is shortlived by Vijayanagara Empire Victory. Those Vijayanagara Emperors belong to Vira Shaiva Sangama Dynasty.

In 15th century, Prauda Devaraya 2 of Vijayanagara Emperor, patronised Arunagiri Nathar of Tiruvannamalai to revive Murugan Worship and they took it to all South Asian Countries, where ever they conquered- Murugan, a war God.

The present rituals are standardised by Arunagirinathar of Thiruvannamalai and followed by these Gurukkals. But the new concept of Kaumaram of Arunagiri, with two consorts of Deivayani and Valli is not followed in Palani.

During Thirumalai Naicker regime in 17th century, Kula Deivam worship was revived all over the kingdom and Pandarams were appointed to do poojas or to assist in poojas.

Hope I answered your query from best of my history knowledge.