of course, the Galaxy is a messy place, and there's no need for the story to end. however, we can do that without plowing a freight train of spiky rape into the story and setting.
the OT, as seen in theaters in the 70s and 80s, is the pinnacle of Star Wars. while much can be added to this, the central narrative must not be subverted. if the Yuuzhan Vong invasion happens, that gives the OT a bad ending. you see, if the Empire had won, they'd be well equipped to fight off the Vong. Imperial Star Destroyers, AT vehicles, and legions of troopers would give them serious trouble, and a working Death Star or two would annihilate their worldships. the only way the Vong could cause so much death and destruction is if the Galaxy is seriously weakened and divided by a successful Rebellion decapitating the Empire's top leadership (ie Endor). of course, no one knew this would happen, but the fact remains, if the Vong invade, the Galaxy would be much better off under an Imperial victory. that does indeed subvert the OT, which I cannot accept.
there's other problems too, such as the fact that the Yuuzhan Vong are immune to the Force, yet they use biotech, and the Force flows through all living things. and there's a thematic clash -- the Vong are essentially the Hostile Alien Invasion trope, yet the Galaxy is full of alien species, so they come from another galaxy. it just doesn't fit, they belong in WH40K as I said.
the only ways I'd accept the Yuuzhan Vong is if 1. they were nerfed and turned into a dangerous species somewhere on the Outer Rim, or 2. their invasion happened centuries or millennia BBY. you could even combine these, by having the invasion happen long ago, with a surviving remnant on some distant planet(s).