It wasn't that they snuck It, but that the higher ups couldn't exactly stop them from entering even if they wanted to.
It would be seen as rebellion against the Leader if they stopped their personnel from seeking positions within the Guardian, same as the Visionary.
Thus, they could only allow them to do as they wished. The best they could do to deter them from overstepping their boundaries was to place surveillance on them and even that would cause problems if done directly.
The situation wasn't exactly the best which annoyed several high ranking Guardians as instead of focusing solely on the threat that plagued the blue planet, threatening their existence, they also had to stay alert against their fellow humans.
It was messed up to know that even during such trying times, humans still had the time to antagonize one another, due to their selfishness and pride.
