Darkoath Flesh vs Desert Ochre

How close are they?

ΔE 17.7, loose: different enough that you should pick on purpose. Desert Ochre is noticeably darker, warmer than Darkoath Flesh.

Can I use Desert Ochre instead of Darkoath Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Desert Ochre is noticeably darker, warmer than Darkoath Flesh.

Can I use Darkoath Flesh instead of Desert Ochre?

The same difference applies the other way round: Darkoath Flesh is noticeably 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.