Iím going to have to agree with Berenger. None of the abilities are strong enough to merit nerfing, least of all LA.
On the Oni: Strength by Skill is pointless. By RAW itís a bonus to Str, which is divided by 2 for the bonus to checks, so you effectively get three extra points of bonus across 20 levels. I donít see Toughened Muscle being of much use outside of unarmed swordsage, and thatís a stretch, since Hammer Meets Nail invalidates WIS. Drive of Strength forces your DM into a narrative corner regarding foreshadowing.
On the Nurarhiyon: Unnoticeability has way too low a check to be useful. Even at high levels, a lot of monsters have massive bonuses to Will, so it doesnít ever become useful. Large Head is a massive, massive liability, especially at low levels, where youíre already behind chained to the massive LA. Cumulative -4 abilities and Scavengerís Inclination donít help either.
On the Arachne: This one seems a bit more balanced, but itís very niche and would probably only work well for RAW abuse like precision damage, as Berenger mentioned.
Overall, thereís a lot of good fluff, but this needs a lot of rebalancing to work. Arachne might be viable in TO environments, but Nurarhiyon loses way too much for a relatively weak ability. And the Oniís racial features actively makes the DMís life harder, unless he simply goes ahead with their plot anyway, and your Oni is killed as an example for how powerful their final boss or whatever is.
ETA: Before anyone brings it up, I saw the zombie apocalypse fluff. The OP doesnít make it clear if these three are the only fantasy races in existence within their setting, so I assumed the normal sword-and-fantasy setting default to 3.x. Feel free to correct me if Iím wrong, OP.