Kaukareldar

In the elder days Elves which escaped from Angband´s dungeons were not always welcome with their old communities, twisted in mind and bent and broken in shape, refugees from Morgoth´s realm often turned out to be traitors against their own will, for the dark lord surely knew how to find out their deepest and darkest secrets and wishes and managed to use them for manipulating his victims spirit.These were the Kaukareldar, most abhorred of them being Maeglin, the traitor of Gondolin.

speculations
The term Kaukareldar only appears in Tolkien´s earliest drafts for the Book of lost tales, however the concept of the elves whose mind and will was twisted and corrupted by Morgoth survived into his later works as the Silmarillion.This concept can be used to explain the existence of evil elves in MERP, as those characters from the court of Ardor or other evil elves from Mordor, Dol Guldur and the East.