No, you can't get to Hoenn after you defeat all 8 gym leaders in Kanto. This is the team I used in SS, and to be honest it really served me well:
Crobat@Poison Barb
Trait: Inner Focus
Nature: Jolly
Moveset:
-Fly
-Cross Poison
-Bite
-Confuse Ray
Typhlosion@Flame Plate
Nature: Modest
Trait: Blaze
Moveset:
-Eruption
-Flamethrower
-Swift
-Focus Blast
Mamoswine@Muscle Band
Nature: Adamant
Trait: Snow Cloak
Moveset:
-Ice Shard
-Earthquake
-Avalanche
-Rock Slide
Ampharos@Choice Specs
Nature: Rash
Trait: Static
Moveset:
-Signal Beam
-Thunderbolt
-Power gem
-Discharge
Dragonite@Dragon Fang
Nature: Adamant
Trait: Inner Focus
Moveset:
-Outrage
-Extremespeed
-ThunderPunch
-Waterfall
Gyarados@Mystic water
Nature: Jolly
Trait: Don't remember XP
Moveset:
-Waterfall
-Surf(needed a Surf Slave)
-Ice Fang
-Earthquake
This was it, it served me well.
Hope I helped :D