Well, their relationship was initially good. When it soured, it only really soured one way, and it was sasuke who was the one holding the grudge. Once Sasuke found out the truth, the hatred disappeared. Since Itachi never really had any hatred, and his lies have been shattered anyway, there's no reason for their relationship to be anything less that what it would've been under normal circumstances. Nevermind that Itachi is a zombie.