Settlements that are classified as penalties are generally not tax deductible. Settlements that are classified as remedial/restorative generally are.
This was no doubt a topic of discussion and planning before the settlement was entered into. The article repeatedly refers to it as a "penalty", but it's unclear if that's colloquial or specifically informed language.
I doubt Monsanto pays an effective tax rate anywhere close to 20%. Further the people who receive the settlement pay taxes on it thus the taxpayer is likely better of.