Most of your Pokemon are HORRIBLE in Ubers. Sceptile is terrible because of its bad defenses and average Special Attack by Uber standards. Swampert, while bulky, can't hit the opponent too hard with its special moves. Aggron's defensive typing is downright terrible in Ubers because of all the Water, Fighting and Ground moves scattered about in Ubers. Absol is too defensively frail and slow to be in Ubers, and not even Sucker Punch can save it. Only Blaziken and Rayquaza see use in there. Really, there's no need to go all-out offensive in Ubers; a lot of Uber teams use status moves to gain the upper hand. Your Pokemon won't like being put to sleep by Darkrai's Dark Void, being paralyzed by Kyogre's/Groudon's Thunder Wave or being poisoned by Lugia's Toxic for instance. You won't be getting anywhere with just Hoenn Pokemon; you need Pokemon from other regions too. If any of my suggestions don't suit this team, I can make a new post to accommodate it.
For starters, Blaziken should use Speed Boost, and Speed Boost ONLY. That's what makes it so good in the Uber environment. It also has little use for Aerial Ace, as a super effective unSTABed Aerial Ace does less than a neutral STAB Flare Blitz/Hi Jump Kick:
-Swords Dance
-Flare Blitz
-Hi Jump Kick
-Protect
Nature: Adamant/Jolly
EVs: 4 HP/252 Atk/252 Spe
Rayquaza's movepool is very good and it certainly has the offensive stats to take advantage of it. But it has better coverage moves than Fly and Thunderbolt. Fly gives your opponent a free switch-in:
-Dragon Dance
-Outrage
-Earthquake
-Overheat
Nature: Naive
EVs: 252 Atk/4 SAtk/252 Spe
Item: Life Orb
or
-Draco Meteor
-Fire Blast/V-Create
-ExtremeSpeed
-Outrage/Dragon Tail
Nature: Naive/Hasty
EVs: 4 Atk/252 SAtk/252 Spe
Item: Leftovers/Life Orb
or
-Dragon Dance
-Outrage
-Draco Meteor
-Earthquake/Fire Blast
Nature: Mild/Rash
EVs: 40 Atk/252 SAtk/216 Spe
Item: Life Orb
or
-Swords Dance
-Outrage
-ExtremeSpeed
-V-Create
Nature: Jolly/Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb
or
-Outrage
-V-Create
-Draco Meteor
-ExtremeSpeed/Earthquake
Nature: Hasty/Naive
EVs: 252 Atk/4 SAtk/252 Spe
Item: Choice Scarf
or
-Outrage
-ExtremeSpeed
-V-Create
-Earthquake
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band
Now, I'll replace the rest of your Pokemon to match up with Uber standards:
Absol for Darkai (because it hits faster and harder, and has Dark Void to give your team an easier time):
-Dark Void
-Dark Pulse
-Focus Blast/Nasty Plot
-Substitute/Nasty Plot
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Leftovers/Life Orb/Focus Sash
or
-Dark Pulse
-Focus Blast/Nasty Plot
-Dark Void
-Trick
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Choice Scarf
or
-Dark Void
-Thunder Wave
-Dark Pulse
-Nasty Plot/Focus Blast
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Leftovers/Life Orb
Aggron for Dialga (sure, Dialga shares 2 of Aggron's weaknesses, but it can take them better):
-Stealth Rock
-Draco Meteor/Dragon Pulse
-Fire Blast
-Roar/Dragon Tail/Thunder
Nature: Modest/Quiet
EVs: 252 HP/56 SAtk/200 SDef
Item: Leftovers
Ability: Pressure
or
-Draco Meteor
-Fire Blast
-Outrage/Brick Break
-Thunder/Bulk Up
Nature: Mild/Quiet
EVs: 252 Atk/252 SAtk/4 Spe
Item: Life Orb/Expert Belt
Ability: Pressure
or
-Rest
-Sleep Talk
-Bulk Up
-Outrage/Dragon Claw
Nature: Careful
EVs: 252 HP/4 Def/252 SDef
Item: Leftovers
Ability: Pressure
or
-Draco Meteor
-Fire Blast
-Thunder
-Dragon Pulse/Stealth Rock
Nature: Modest/Timid
EVs: 252 HP/252 SAtk/4 Spe (Choice Specs) or 56 HP/252 SAtk/200 Spe (Choice Scarf)
Item: Choice Specs/Choice Scarf
Swampert for Palkia (because Palkia hits faster and harder than Swampert can):
-Surf
-Spacial Rend/Draco Meteor
-Thunder
-Fire Blast/Outrage/Draco Meteor
Nature: Timid/Hasty
EVs: 4 HP/252 SAtk/252 Spe
Item: Choice Scarf
or
-Surf
-Spacial Rend
-Aqua Tail/Outrage
-Fire Blast/Thunder
Nature: Hasty
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb/Expert Belt/Lustrous Orb
or
-Draco Meteor
-Hydro Pump/Surf
-Spacial Rend
-Thunder/Fire Blast
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Choice Specs
or
-Substitute
-Focus Punch
-Spacial Rend
-Thunder/Fire Blast/Surf
Nature: Hasty
EVs: 100 Atk/156 SAtk/252 Spe
Item: Leftovers/Expert Belt
or
-Aqua Tail
-Outrage
-Spacial Rend/Draco Meteor
-Fire Blast/Thunder
Nature: Hasty
EVs: 252 Atk/4 SAtk/252 Spe
Item: Lustrous Orb/Life Orb
Sceptile for Shaymin-Sky (it's faster and hits harder):
-Substitute
-Leech Seed
-Seed Flare
-Air Slash/Hidden Power (Fire)/Earth Power
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Leftovers
or
-Seed Flare/Leaf Storm
-Air Slash
-Earth Power
-Hidden Power (Ice/Fire)/Growth
Nature: Timid/Modest
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Specs/Choice Scarf/Lfe Orb