ΔE 33.2, loose: different enough that you should pick on purpose. Mortarion Grime is noticeably lighter, more saturated, cooler than Dark Skin Shade.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 33). Mortarion Grime is noticeably lighter, more saturated, cooler than Dark Skin Shade.
The same difference applies the other way round: Dark Skin Shade is noticeably darker, more muted, warmer.
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 Dark Skin Shade on the colour wheel See Mortarion Grime on the colour wheel
All matches: Dark Skin Shade equivalents · Mortarion Grime equivalents