Your question is specifically pertaining to adding saline water to soils. Saline water is mainly understood as NaCl (see WIKIPEDIA).

It depends upon the the type of soil in question and concentration of salt solution. Compaction behaviour of coarse grained soils (sand, gravel) may not get affected since physico-chemical interaction between soil solids and pore water is insignificant (suction changes are important as water content increases), whereas the effect of saline water on dry density and water content of fine grained soils (particularly clays composed of montmorillonite) can be significant (you are aware of this effect). An increasing concentration of salt in pore water tend to cause a decrease of the OMC and an increase in the max. dry density. Some contradicting effect may be noticed particularly in case of kaolinite (please check published papers on kaolinite in Can Geotech J and elsewhere).

For reasons please also see some classic papers published in NATURE by Warkentin and later by Yong.