ΔE 12.8, fair: the same colour family, but not a straight swap. Mortarion Grime is a little lighter, more muted, warmer than Military Shader.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Mortarion Grime is a little lighter, more muted, warmer than Military Shader.
The same difference applies the other way round: Military Shader is a little darker, more saturated, cooler.
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 Military Shader on the colour wheel See Mortarion Grime on the colour wheel
All matches: Military Shader equivalents · Mortarion Grime equivalents