I sincerely doubt the two artists were reported. The NCMEC website paraphrases the statute linked in lj_biz. The statute deals ONLY with visual images that are indistinguishable from an actual child (anyone looking at the image would think they were looking at a real child) OR is of an identifiable minor (something in the picture shows exactly which actual minor was victimized). The images in question were not of an actual person(s), nor could you mistake the images as being of an actual person. They don't meet the statutory definition of child pornography, so it would be phenomenally stupid of LJ to report them. They said they reserved the right to ban material that WAS LEGAL, and that is what they did there. It may meet LJ's expanded definition of child porn, but it doesn't fall under the statute.
Further, a "minor" under the statute is a PERSON under the age of 18. Fictional characters CANNOT be a person under the law. To make a point: A fetus in the womb is NOT considered a person under the law. There is NO POSSIBLE WAY a fictional character would be afforded the status of a person under the law, when a fetus is not.
I gave a detailed description of what LJ's response does for them in the greater scheme of things on my LJ, so I won't go into here. But in general, in their responses they MUST make it appear that they are concerned solely with the illegality of the material they are banning, when, in actuality, they have said they WILL be banning material that is legal and protected by the First Amendment. That's what happened with the ponderosa121 and elaboration, and they are using illegal child porn as a smoke screen to hide their real actions. 6A's actions are brilliant from a company and public perception standpoint, and they have ensured that the only people who know what's really happening are the one's with a vested interest in delving into the issue. I wouldn't worry about reporting or the law because it is on fandom's side, as it stands now. 6A is just directing attention away from what they are really doing.