This partially depends on where you place 'ethics'. If ethics is worried about "what's right" in Eliezer's terms, then it's not relativist at all - the pebble-sorters are doing something entirely different from ethics when they argue.
However, if you think the pebble-sorters are trying to answer the question "what should I do" and properly come up with answers that are prime, and you think that answering that question is what ethics is about, then Eliezer is some sort of relativist.
And the answers to these questions will inform the ques...
Less Wrong is extremely intimidating to newcomers and as pointed out by Academian something that would help is a document in FAQ form intended for newcomers. Later we can decide how to best deliver that document to new Less Wrongers, but for now we can edit the existing (narrow) FAQ to make the site less scary and the standards more evident.
Go ahead and make bold edits to the FAQ wiki page or use this post to discuss possible FAQs and answers in agonizing detail.