R2 dlc always need to use EU account to redeem.. they are on their own, not like R1 and R3 sometimes can work with each other.
DLC code always have to use the correct region's account to redeem, regardless whether one region's DLC is compatible with another region's base game.
R2 and R3 are sometimes compatible as well. Basically R1 and R2 are always separate from each other, not cross-region compatible. R3 is sometimes separate from all other regions (especially the multi-language version games), sometimes take from R1 (so it's compatible with R1), sometimes take from R2 (thus compatible with R2).