The Leaf strikeforce is being assembled by Shikaku on short notice after a Sand messenger brings him the news of Gaara's kidnapping, and this informs the context of who'll they'll be bringing with them.
I find it decently likely Shikaku knows about Orochimaru, but I also think that Shikaku bringing Orochimaru into the squad would involve quite a few hurdles:
- Getting Orochimaru to agree. Might not be a problem, but also might. Orochimaru might demand concessions.
- Getting everyone else to accept it. Most of the rest of the strike force probably don't know Orochimaru was there, and to suddenly hear that a reviled missing-nin S-ranker is now your teammate is bound to cause problems.
- Team cohesion. Everyone's going to be watching out for Orochimaru to betray them, and plotting how to strike back in turn. These machinations detract from the strike force's overall ability to coordinate properly.
So it's not
totally against Orochimaru being there, he's still an S-ranker which means he's got a lot of firepower to add, but I can easily see Shikaku deciding the other way.