Saline-sodic dispersion

Yes they do. The only difference is that saline-sodic soils have (besides high sodium) an additional problem of high salinity. So, they are the worst possible type of soils for plant growth.

Just for my own clarity, "high salinity" is measured as "high electrical conductivity" (>4 S/m)?

Yes, that is correct.... but the units are dS/m, so electrical conductivity needs to be higher than 4 dS/m for a soil to be classified as saline