You might be right that you can aproximate a quadruped with a horizontal capsule(thats why I will use Mover becouse it lets you use any collisions even if they are not a upright capsule)
but my quadruped also will also fly(edit: also climping slopes/stairs and rotating in its place), so its something like the fish you where saying.
I thoght on a solution of making the character(Edit: pawn with Mover) have 2 collision spheres (one for the back and another for the front) so now rotation is just a moving one shpere. This is theoreticaly posible with Mover but I havent test it yet.
Edit: sorry for the spelling errors, I am not native english