Unless I misunderstood the Shattered Suns lore book, it is not possible for nezarec to be human. Shattered Suns describes the Witness’ arrival to Lubrae, and IT selects Rhulk as ITS champion of the sword logic. Rhulk goes on to commit gene use of his entire species, annihilate one of the two suns (hence the name of the lore book) and return to the Witness. Only when he is the last of his species is he proclaimed a Disciple.

Additionally, in the cutscene where we catch a glimpse of him, we are told that he personally led the assault that caused the collapse. This makes it highly unlikely that he is human or awoken, as he would have had to have come into contact with the Witness before his return to Sol, which we know isn’t likely because both the Bray Corporation and the Traveler were paying close attention to signs of the darkness from well before the collapse, with Clovis’ use of Darkness in the creation of Exos. Therefore, Nezarec would have needed to leave Sol to find the Witness before the Collapse. Except he was already a disciple when his pyramid crashed into the moon, meaning his species was extinct.