Hi, it's nice to meet you! I'm always down for establishing pre-game CR, and it is definitely likely that Sion and Giovanni would at least know of/about one another.

Before he turned Company administrator, Sion was an on-the-ground enforcer, so it's possible that they could have done Awful Things together-- while Sion has resistance leanings, he's built something of a reputation for himself by being brutally efficient in the field, and could also be categorized as a 'genetically engineered monstrosity', haha.