@Maze247365The Guyvers armour has been shown to be extremely resistant to anything short of Enzyme-type acid, your Zerbebuth example is a good one as going by what has been seen Xenomorph blood has roughly the same strength as what he fires from his horns so while a bit wont do much, enough in the right places will start affecting the Guyvers combat ability until they can heal. The vibrational blades would also be very effective as long as the Guyver is quick enough to keep any acid away from the base of the weapon.
Xenomorphs getting into any of Chronos HQ's wouldn't happen unless they were allowed to, remember their security starts at "paranoid" and goes up from there. That said if some Facehuggers did get in and could infect processing subjects before they properly develop the link to the Zoalords you might have the start of a ZoaAlien problem especially if you throw some of the more powerful Hyper types and Lost Numbers into the chestburster mix.
A Guyver/Alien crossover could be an interesting fic but the difference in power levels means you would have to get creative to make the Aliens a threat without having the story breakdown as soon as you apply basic logic to the situation.