ΔE 15.8, loose: different enough that you should pick on purpose. Rakarth Flesh is a little darker, warmer than Undead Skin.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Rakarth Flesh is a little darker, warmer than Undead Skin.
The same difference applies the other way round: Undead Skin is a little lighter, 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 Undead Skin on the colour wheel See Rakarth Flesh on the colour wheel
All matches: Undead Skin equivalents · Rakarth Flesh equivalents