I believe you need to clarify Hawking's comments - in particular to ask
"theoretically - what is the smallest black hole (event horizon) you could conceivable create and could it be Planck size 10 ^ -42 metres or less?"
If Hawkings where answering that question he was talking about the cosmic foam with the possibility part of what forms spacetime - apart from virtual particles are incredibly tiny black holes that also wink into and out of existence everywhere all the time.
I seem to remember that was part of the context to his statement. The Earth would become a black hole if it where crushed to a diameter of an inch, so maybe Hawkings thought what would happen if an atom or subatomic particle where crushed on that scale too? Could it also become a black hole and if so - if its is so minute could it simply drop out of our existence all together? If its event horizon was trillions of times smaller than the diameter of a quark would it to all intents and purposes simply not be there?
Perhaps that is dark energy - simply super crushed energy carriers that are trillions and trillions of times too small for us to possibly every detect?
/end_spectulation_mode