Slight Spoiler Alert:
According to the site, "the cameo would've taken place at the very end of the film and was originally billed as an "alternate ending" (I'm assuming with the hope they could convince Schwarzenegger to come back).
"The human survivors are sitting bloody and beaten in the jungle. The silence is interrupted by a vibration that grows until it sounds like a freight train is bearing down. Once the dust cloud settles a Predator ship is revealed."
The door opens and dozens of Predators file out. The humans are screwed now. There's nowhere to run. Even if there was, they don't have the energy for any more fighting. The Predators don't attack, but part with two single-file lines on each side of the door. Their leader, with armor covered in "trophies," exits and walks towards them. He slowly removes his helmet to reveal...DUTCH. "Not bad kid...not bad at all." SMASH TO BLACK.