In Eberron lore a Khoravar (one of the pure half-elves) cannot join the Undying Court, nor be elevated to the status of nobility. Lore-wise, Helf Favored Souls probably shouldn't have the Undying Court option. That said, a Khoravar that displayed incredible skill or in some way attracted the attention of the Undying Court might be granted some form of favorable status.
A half elf who practices the codes of a paladin only as a dilettante would most definitely not make any impression on the Undying Court.