The spark or arc, will jump to the closest ground it can find, doesn't matter how many grounds you have around the electrode, it will go to the closest. If you drill a hole in the ground, the arc will jump around the opening on the sharp edges, it will never go through the hole. All the hole will do is introduce a slightly extra bit of mixture at the arc.
Indexing the plugs so the open side of the ground is facing the chamber will do more good then a hole will, but you will never see the gains of your hard work indexing them on a truck.
I've run lots of plugs and distributors on my machine, I've never seen the arc change with different plugs.
