When the Vong decided to come out of nowhere and provide a new storyline to the Galaxy, Nom was an advanced scout. Presumably this rank had nothing to do with the Executor, and may have been pronounced differently depending on if he killed people or just managed the estates of dead relatives. Nom Anor was part of a political caste, and became an Executor. Nom Anor was one of the most notable Yuuzhan Vong when they did that galaxy-conquest thing.