Yes,That Stop skill comes from Blue Acidus and the Wind Attack makes you pain.I think Fire Armor is the best choice not Garm nor Disguse because you can avoid fire skill from Gold Acidus/Red Ferus and earth attack from Green Ferus.Whoever to play there,just don't mob 3 or more Blue Acidus,It's not worth because Stone Buckler and Magni Cap dropped by Gold Acidus and Red Ferus.
@about the reduction
15% from Dragon Breath and 30% from Dragoon it never make 45%.
example 1k damage taken:
15% reduction make it 850 damage taken
30% more reduction make it 595 damage taken
If it as you said if will become 550 damage taken
or plus deviling make it 95% makes you took 50 damage only instead of 288 damage taken.
That's not include defense reduction(hard def by % and vit def by point).
@Edit
Just realise what are you asking for 'Is it the same function make it stacking or just come after the other reduction gear?'
I think all above my answers not totally rite but yes it never stack with Deviling function.