This looks like a good team. Dragon monotype is fun, and with the fairies coming soon from XY, there's not much time left to spam Dragons.
That being said, there is a lot that can be changed with this team to make it a little bit more competitively viable. As most Dragon spam is offensive/hyper-offensive, perhaps you should consider, as The-Me said, a RockChomp. The set that I recommend is as such:
@ Focus Sash
Trait: Rough Skin
EVs: 252 Atk / 252 Spe / 4 HP
Jolly or Naive Nature
- Stealth Rock
- Swords Dance / Fire Blast
This Garchomp is awesome for your team because it keeps doing the things your original set does, but also lays a hazard and beats opposing leads. Rough Skin breaks opposing sashes, and with Swords Dance, you can sweep whole teams that don't pack a powerful Choice Scarf. Earthquake even 2HKOs Ferrothorn at a +2! Fire Blast can offer more power immediately for Ground-neutral Steels, and beats Ferro and Skarmory exceptionally well. A Focus Sash of your own does cause a bit of a drop in power, but will let you guarantee either a setup opportunity or rocks on the opposing side of your field. I cannot urge you to use this set enough.
When it comes to Dragonite, I really think you should either (a) slap a Choice Band on him or if you're opposed to that, run Roost instead of Earthquake. Except for Heatran, Earthquake gives you no additional coverage, and you need Roost to maintain survivability if you're adamant about running Life Orb. Also, Multiscale on Dragonite, won't disappoint, please use it.
Salamence is just fine for the most part, but I'd consider replacing Roost, as Mence has little surviving ability anyway. Dragon Claw is great if you don't want to lock Outrage, and Earthquake nails those annoying Heatrans that would cold stop your Mence sweep.
Hydreigon has a few options. First off, dual scarves on Pokemon with little offensive synergy doesn't make a lot of sense, so perhaps a Choice Specs set is preferable, so you can hit like a truck against those that don't resist Draco Meteor. Another option is a Substitute Hydrei, which is actually quite good and has impeccable coverage.
Haxorus is not an amazing Choice Scarfer to begin with, but I see what you mean by Jolteons. If you're willing to change up the Scarf position a bit (maybe switch with Mence?), you can run the amazing Swords Dance Haxorus, who will break the walls that you have trouble with, almost guaranteed.
Kingdra is... a weird choice. You should always
run Swift Swim on Kingdra in OU, as it's only niche (beating Rain Teams) is completely canceled if you run Sniper. Flail is so useless it's not even funny. Iron Head doesn't make a lot of sense, as Ice types will still kill your team regardless of whether you have an admittedly underpowered Steel move or not. Dragon Dance is perfectly usable on Kingdra, and if you're sure you don't want to do that, at least run Yawn or something.
Please make Garchomp a Rocksetter.
Dragonite should either get a Band or Roost.
Salamence should nix Roost and go with Earthquake or Dragon Claw.
Hydreigon should be Specs or Substitute.
Haxorus is mostly fine.
Kingdra should ditch Iron Head and Flail, and run something with more utility.