No one is immune to Genjutsu. Sasuke caught him in his Genjutsu but Orochimaru simply wasn't even tickled by it. These are manga facts and I don't understand why you're arguing with it. And I don't see any point in bringing Deidara in here.What I meant was that, the ones to favor Orochimaru always bring the argument of Orochimaru being an intellectual scientist, genius etc, although this doesn't grant him immunity to techniques. Deidara trained much longer than Itachi and more intensively, and despite that fact he countless of times fell prey to Sasuke's genjutsu, which is even inferior to Itachi's.
@Bold.
While the theory that Hebi Sasuke used his Curse Mark in conjunction with Sharingan to resist Fushi Tensei is not only just a hypothesis but also doesn't matter in this case due to Sasuke possessing it, and Fushi Tensei =/= Sasuke's genjutsu. Irrelevance.
Capisce?
It's not a hypothesis. Re-read their fight. Sasuke clearly combined Sharingan and CS powers to resist Fushi Tensei. But it doesn't matter, since pure Genjutsu isn't doing shit to Orochimaru, as we've already seen.