(Dragonite) @ Yache Berry Ability: Inner Focus EVs: 252 HP / 252 SpA / 4 SpD Modest Nature IVs: 0 Atk - Rain Dance - Surf - Thunder - Hurricane
(Hydreigon) @ Choice Scarf Ability: Levitate EVs: 252 SpA / 4 SpD / 252 Spe Timid Nature - Dragon Pulse - Dark Pulse - U-turn - Fire Blast
(Altaria) @ Altarianite Ability: Natural Cure EVs: 252 Atk / 4 SpA / 252 Spe Lonely Nature - Dragon Dance - Fire Blast - Earthquake - Roost
(Haxorus) @ Dragonium Z Ability: Mold Breaker EVs: 252 Atk / 4 SpD / 252 Spe Adamant Nature - Dragon Dance - Outrage - Earthquake - Poison Jab
(Drampa) @ Assault Vest Ability: Sap Sipper Shiny: Yes EVs: 248 HP / 252 SpA / 8 SpD Modest Nature IVs: 0 Atk - Draco Meteor - Hyper Voice - Fire Blast - Focus Blast
(Salamence) @ Life Orb Ability: Intimidate EVs: 252 SpA / 4 SpD / 252 Spe Timid Nature IVs: 0 Atk - Fire Blast - Dragon Pulse - Hidden Power [Electric] - Hydro Pump Tell me if and how I can improve
You should change dragonite from special to physical because he has a higher physical base stat. Evs for dragonite should be 252 Hp, 252 Attack, 4 Sp.D. Moves for Dragonite could be Waterfall/Aqua tail (Waterfall for accuracy and Aqua tail for power) instead of Surf, Aeril Ace/Sky Drop (aerial Ace for never miss and Sky Drop for a safe round) instead of Hurricane, Thunder Punch instead of Thunder and Roost/Dragon Claw (Roost for Healing and Dragon Claw for Dragon coverage) instead of rain dance.
Other than that everything looks good.
Hope this helps