ΔE 25.4, loose: different enough that you should pick on purpose. Orc Flesh Wash is noticeably lighter, more saturated, cooler than Mortarion Grime.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Orc Flesh Wash is noticeably lighter, more saturated, cooler than Mortarion Grime.
The same difference applies the other way round: Mortarion Grime 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 Mortarion Grime on the colour wheel See Orc Flesh Wash on the colour wheel
All matches: Mortarion Grime equivalents · Orc Flesh Wash equivalents