X6 Rear Shock Tower
 

Is the outer hole on the tower ever used for any type of tracks or condition?

Possibly, Mike.

When a new tower is developed the team would have had many prototypes all with holes in different locations, some work and some dont, what you will have now is a combination of the ones that worked best on different tracks/surfaces.

On the 3 gear car i ran on the outer holes at times this was with the old tower too though ;)

The 2 outer holes on the 4-gears tower are the same that the 2 inner holes of the old 3-gears towers, that were used every time.
So you need those in order to mimic older setups.