ΔE 5.0, very close: most people won’t see a difference side by side. Nurgle's Rot is a little lighter than Yellow Green. They are different kinds of paint: AMMO by Mig Yellow Green is an opaque base/layer paint and Citadel Nurgle's Rot is a technical paint or medium, so they won’t behave the same on the model even where the colour is close.
Yes, for most jobs. Very close match (ΔE 5). Nurgle's Rot is a little lighter than Yellow Green. They are different kinds of paint.
The same difference applies the other way round: Yellow Green is a little darker.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Yellow Green on the colour wheel See Nurgle's Rot on the colour wheel
All matches: Yellow Green equivalents · Nurgle's Rot equivalents