That rule is only sorta true. You are right that "no tape on striking surface" is found nowhere in the MOA. Its one of those hidden rules of Dag. Technically, you CAN have tape on the striking surface, but you A) have to cover your weapon in cloth, and B) have it pass the hit test. The reason you had that notion is a good one. Tape not only makes a weapon hit hard, but it looks like crap and it will tear the foam up.
Also: Put silver tape on non-striking edge of single edged weapons only.