ΔE 15.4, loose: different enough that you should pick on purpose. Gravedigger Denim is noticeably darker than Dawnstone.
Can I use Gravedigger Denim instead of Dawnstone?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Gravedigger Denim is noticeably darker than Dawnstone.
Can I use Dawnstone instead of Gravedigger Denim?
The same difference applies the other way round: Dawnstone is noticeably lighter.
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.