Yes, it's trivially possible.

feature c2sc {
    sub [...I J...] by [...I.sc J.sc...];
} c2sc;

feature salt { # placed in 'salt' for access in Illustrator
    lookup alternates {
        sub [I J I.sc J.sc] by [I.alt J.alt I.sc.alt J.sc.alt];
    } alternates;
} salt

feature ss01 { # duplicated as a stylistic set for access in InDesign
    lookup alternates;
} ss01;

André

Features are applied in order. So if your small caps feature comes first, make sure your stylistic alternate code changes both caps and small caps to the alternates. And if your alternate features comes first, make sure your small caps code "small-capifies" both the standard and the alternate letters.

Thank you both agisaak and eliason!!

feature salt {
lookup alternates {
sub [I.sc J.sc Igrave.sc Iacute.sc Icircumflex.sc Idieresis.sc] by [I.salt.sc J.salt.sc Igrave.salt.sc Iacute.salt.sc Icircumflex.salt.sc Idieresis.salt.sc];
} alternates;
...
}salt;

which sits after the smcp feature.

Legends!