Violent Vermillion vs Inferno Orange

How close are they?

ΔE 15.4, loose: different enough that you should pick on purpose. Inferno Orange is noticeably darker, more saturated than Violent Vermillion.

Can I use Inferno Orange instead of Violent Vermillion?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Inferno Orange is noticeably darker, more saturated than Violent Vermillion.

Can I use Violent Vermillion instead of Inferno Orange?

The same difference applies the other way round: Violent Vermillion is noticeably lighter, more muted.

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.