Dark Ochre vs XV-88

How close are they?

ΔE 8.9, close: similar, with a visible difference side by side. XV-88 is a little lighter, warmer than Dark Ochre.

Can I use XV-88 instead of Dark Ochre?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). XV-88 is a little lighter, warmer than Dark Ochre.

Can I use Dark Ochre instead of XV-88?

The same difference applies the other way round: Dark Ochre is a little darker, 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.