There are a few reasons why sharing Scouting gear with ninja would make sense.

It would spread gear more fairly, with two classes competing for each type instead of three for Aiming and one for Scouting.

Dancer's weaponry (chakrams and throwing-knives) would do slashing damage like ninja, not piercing like bard/machinist.

And visually, Scouting has more gear suited to dancer glamours, at least in my opinion.