I read, i dont remember where, that the first guitarist that ever played tapping was either Eddie Van Halen or Randy Rhoads. During the 70's when they had their war about
who is the best guitarist on the planet, one of the tricks they applied to win the battle was tapping but noone can tell for sure who was the first one who used it.

I read something like this a long time so i may not remember right, if you know anything about this clear it up