TH, the latest snip almost gave me heart attacks from the fluff in at least 3 different sections. I don't know whether I should blame you or congratulate you.
This is pretty much confirmed IMO. Monochrome Concerto (SAO Floor 3 side story, new chapter parts released in magazines right now) have shown giant spiders as Mobs. On a side note, if the SAO veterans hear about elves they'd probably not think of the epic killing-machines as the locals sees them but go "Elves? Wait, you mean those guys from before Floor 10 of Aincrad? Sure, they had some sweet loot, but those weren't that hard to beat..."