Lead with Deoxys-S, not Ferrothorn. Deoxys-S has that Sash, so it can set up without worrying later in the game about Entry Hazards breaking that Sash. And give it either Superpower, Focus Blast, or Ice Beam. Superpower hits Pokemon like Dark Arceus and Tyranitar for solid damage, while Focus Blast doesn't hit Tyranitar as hard it will probably allow you to not have to diversify your offensive EVs. Although watch out for that accuracy. Ice Beam allows you to hit the Dragons and Lugia for more damage. I'd also replace Toxic for Thunder Wave and Spikes for Stealth Rock. The first change I found to be helpful as a going away "save the rest of the team instead of doing average damage with Psycho Boost" as with Deoxys-S's Speed stat it can get in Thunder Wave before Scarfers and help the rest of the team take them down. This is very useful for the dreaded Palkia. As for the Spikes for Stealth Rock, I'm going to suggest replacing Ferrothorn later, and Stealth Rock is more important in the Ubers enviorment due to the number of Flying types.
Now for Arceus. Steel-Arceus is good but I don't think it supports the team much. I would consider swapping it out for Fighting-Arceus, which handles your huge Dark Arceus weakness.
As I said, I was going to suggest replacing Ferrothorn. Most things in Ubers you'll see carrying Fire Blast. And Zekrom will be carrying HP Fire. Pretty much everything besides Kyogre can counter it. I'm going to suggest replacing it for either Chansey or Blissey (I prefer Chansey, but if you like Leftovers healing and slightly bigger Wish passes, Blissey is your gal). These two keep Ferrothorn's ability to destroy Kyogre, while also adding in help against such foes as Palkia. Chansey/Blissey are excellent Pokemon in Ubers, taking down all non-Mewtwo Special threats.
Giratina needs a nature.
Rayquaza I'm going to say no on Air Slash. Not only is it Special, but also Flying coverage isn't the greatest in Ubers unless it is with a Brave Bird from Ho-oh (which just does amazing damage to stuff that Sacred Fire isn't going to hit as hard). Give Rayquaza either Stone Edge (for Lugia and Ho-oh) or Dragon Claw for when you need to hit for a Dragon attack but you know your opponent has a counter to Rayquaza.
Mewtwo... definately go for Timid.