ΔE 20.0, loose: different enough that you should pick on purpose. USAF Brown is more muted, warmer than Undead Skintone.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). USAF Brown is more muted, warmer than Undead Skintone.
The same difference applies the other way round: Undead Skintone is 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 Undead Skintone on the colour wheel See USAF Brown on the colour wheel
All matches: Undead Skintone equivalents · USAF Brown equivalents