Haxorus: Replace taunt with dragon dance/sword dance. Then keep only brick break instead of rock slide because you already covered ice. Place in a huge-coverage move like Earthquake(it covers 5 types).Also you can add one more hiiting move instaed of taunt and scarf him.
Hydreigon: Hmm, taunt is still unescessary because he's a sweeper. Add instead hidden power [flying/psychic] or If you haven't add Dragon tail, even if your nature is modest. You can use it either as an offensive move which switch out the opponent, either as defensive ''Roar''. Other options are Thunder wave, Toxic, Incinerate and U-turn, they will be not sweeping, but mostly technical. If either here you chose to put 4 hitting moves give a choice item.
Volcarona:Since you are using quiver dance, fiery dance is completely Inutile!!!
Place instead solarbeam/flamethrower for more STAB or combo and coverage. Also a good idea is to give him heat rock since you are planning a sunny weather, but this one-person sunny day team is a bit surprising. OK it helps Volcarona but might cause troubles to his team-mates. Better place it to a sunny-day team it will be really the best thing to do, because all his team is raised by sun and he doesn't need sunny day if someone has drought.
Snorlax: Place Return instead of heavy slam. Even if your heavy slam hits the max. power (120), Return will be stronger (102+STAB=153). In the other hand you can place Belly Drum for direct attack raising instead of curse.
Dragonite: Definitively, since you have roost you can't have multi-scale so keep Inner-focus it protects you from some situations, but they are quiet rare... Your set is really perfect! Bravo! Bravo!
Metagross:Since you're using choice scarf take out this hammer arm! It copmlitely destroys choice scarf's strategy. Place instead something like Ice punch for more coverage. Also if you ever decide to take out his choice scarf give him agility...
Hope this helps,