Can equipped apparel make hurtboxes smaller or bigger?
Solution 1:
According to Splatoon Reddit, it seems that no, the difference is only aesthetic.
Shoes doesn't make your inkling taller or shorter, it just kinda shortens your inkling's legs. Your height from the ground, and hitbox therefore, are exactly the same as they would be with any other shoe.
Also from another discussion on Reddit:
No, there is no gear in the game that makes your hit box bigger
And since hairstyles don't change the hitbox, probably it's the same with shoes.