He could have uses for Itachi, but there are so many problems with that situation that Vincent will likely never come near it. First off, Itachi is on a team which is not random incident to a knight and runs the risk of upsetting an entire team. If I recall correctly, Vincent even knows that KK was the one who put the team meeting together from way back when, so it's not like Emerald isn't a proactive team, either.

Then, Itachi can restrain himself! He is really rather adept at self-control, so Vincent knows that if he is going to piss someone off between him and Sasuke . . . Well, Vincent would rather gun for pissing off Itachi, because Sasuke is infinitely more likely to fly off the handle and make it a situation. Not that Itachi isn't terrifying in his own right and has extreme potentials to make a situation go rather badly, but Vincent likes minimized publicity and to be able to run damage control as he likes. If Itachi attacks him, he will be quiet and discrete, because it's between them whereas Sasuke could do it in right in the ring and create an entire scene.

So, that pretty much eliminates using Itachi on his own! Vincent prefers to use him as an accessory to deal with Sasuke and will often angle his actions and behaviors towards that end goal, rather than trying to cut any sort of deal between him and Itachi. Granted, that would change if Itachi seemed open at all to Vincent, because Vincent would enjoy having the pleasure of working with him and they could work really well together . . . But it's also much, much easier to go with the sibling that is more easily manipulated.

I am indulgent, sue me. What does Itachi know of Vincent's plans? And what does he think his goals are?