I would be very suprised if Andreesen Horowitz would be ingnorant of this - most likely that would indicate that they're inept in some way.

That leaves complicity. They did make millions (50M?) in a very short period.

The cool thing to do would be for AH to step in and tell the engineer that they'll pay him for what his stock should have been worth, taking it out of their payout.

That would be a classy move.