It is pretty circumstantial as how the deal comes about and how willing without being forced Itachi would be . . . Hmm, at the most, he would want Itachi to act as a counterbalance to keep Emerald from having it out for his team, if not him. After that, he would likely use Itachi for quests that involve others that he doesn't want publicly aired. Like the quest to heart-dive Three, Vincent had to pick people that wouldn't see/question that Vincent was absolutely lying to them about what he was questing for. Itachi is, of course, keen enough to put two and two together, so he would just leave it with Itachi knowing better than to make that realization public. Still, it's dicey to have someone that intelligent on board, so Sasuke is preferred once again.

In more relevant terms, considering their history, Vincent would definitely work with Itachi to minimize Sasuke getting himself into trouble. Rather than trying to actively use Itachi for something, he would be more willing to pander to what Itachi wants to do while lifting information and perspective for him. It would be another side to Aather and a set of eyes on the situation that Vincent really wouldn't mind. If there's anything that Vincent can never have enough of, it's information. So, that would probably be the most that would come of that situation.

We could bang out that information stuff here if you wanted? I can run over what Vincent has publicly done, then we can bat back and forth.