ΔE 10.7, fair: the same colour family, but not a straight swap. Scarlet Red is a little lighter, more saturated than Rust.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Scarlet Red is a little lighter, more saturated than Rust.
The same difference applies the other way round: Rust is a little darker, 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.
See Rust on the colour wheel See Scarlet Red on the colour wheel
All matches: Rust equivalents · Scarlet Red equivalents