ΔE 25.2, loose: different enough that you should pick on purpose. Ruby Red is much more muted than Baal Red. They are different kinds of paint: Citadel Baal Red is a one-coat contrast-style paint and Nocturna Models Ruby Red is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Can I use Ruby Red instead of Baal Red?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Ruby Red is much more muted than Baal Red. They are different kinds of paint.
Can I use Baal Red instead of Ruby Red?
The same difference applies the other way round: Baal Red is much more saturated.
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.