You’ve asked an interesting question, I’ll try to make it as simple as possible.
+80% poison damage is global
12 Acid damage only applies to weapon damage (ie blood burst) and thus DEE on its own will receive none of this. With blood burst you will receive this value modified by the % weapon damage on the skill. At 1 point in blood burst, the burst will deal 3% of the 12 acid damage, for example.
I assume your final example, the 600 poison damage, refers to tainted eruption, the acid proc on abomination. This is an active skill that fires 15% of the time when you attack using the skill to which you have bound it.