ΔE 27.2, loose: different enough that you should pick on purpose. Sulfur Ore is noticeably lighter than Skullcrusher Brass.
Can I use Sulfur Ore instead of Skullcrusher Brass?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Sulfur Ore is noticeably lighter than Skullcrusher Brass.
Can I use Skullcrusher Brass instead of Sulfur Ore?
The same difference applies the other way round: Skullcrusher Brass is noticeably darker.
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.