The bonuses are additive.
So, 30% and 100% = 30% + 100% = 130% (bounded to 99%)
Also, all to-hit chances are bounded by 1% and 99%.
No matter how easy it is to hit something, there is always a 1% chance that you'll miss.
My brother's very first shot in combat (after 150 turns of buildup) was his Crystalline tech battleship
missing a
planet!
The only way to get 100% to hit is with a religious talisman, and that ignores all bonues, guaranteeing 100% in every case.