Geosets have a flag whether they are selectable. Collision shapes are for selection through rectangle drawing only.
Collision shapes are only for optimize the calculation for missile collision and these things, has nothing to do with the selection. A model is selectable without a collision shape.
Missiles fly to the offset specified in object editor, attack range, area range splash etc. depend on the collision size from object editor. The model does not hold traffic gameplay influence. So I do not see how a "hit box" would help.
edit: Tested, it does somehow influence selectability, though only imprecise and maybe via the extents.
Yes, the Collision shape helps the selection circles around the model, not the selection!