The implication of the scene between Bram and Frank is that they are taking the box with Locke's body to Jacob and/or Richard so that they will know who's body Anti-Jacob will appear as. So it does look as if they were expecting to find Jacob there. If they were looking for Anti-Jacob, why would they carry around Locke's body? Presumably he would already know that he had taken Locke's form.
Implied maybe, it was left ambiguous for a reason. Not one of them ever says they're going to see Jacob at anytime. It very well may turn out to have been Jacob they were looking for at the cabin, but as of now we do NOT know that for a fact. What we do know is the ash was used as a binding/protection ring--per Darlton on the season 3 DVD's and we do know Christian and Claire were the "people" seen there. We do know Christian is dead and Darkman has the powers to control, take over, use the dead. All that points, imo, to Darkman being trapped at the cabin, not Jacob.
Locke's body was needed as proof and as the big reveal.
The scene at the cabin was broken up by the Ilana and Jacob flashback (if indeed these were flashbacks of Jacob, which could be debated - more on that later), where he asks her for help. At this point we can assume that she is working for him, and that he somehow gave her instructions of some sort, like the shadow question. The fact that she later goes to the statue, where she was directed to go by the picture in the cabin, and finds Richard and asks him her question strongly implies that they are on the same team.
It may very well have been Anti-Jacob in the cabin that we saw, but I wouldn't say for certain. In the season 3 DVD commentary for "Cabin Fever", Cuse and Lindelof did say that the ash acted as a sort of binding spell for Jacob, meaning that Jacob was in the cabin at that time. Of course, they could have been misdirecting the audience or have simply changed their minds about it. It would be interesting if Ben somehow managed to trap Jacob in the cabin in order to get some sort of control over him. When Ben
Lost power, Richard could have set Jacob free, which would have allowed him to return to the statue and visit Sayid several months later. Of course, the Locke, Jack, and Sun and Jin flashbacks could have coincided with this entrapment, which would argue against it.
The other possibility, which I mentioned earlier, is that these visits were made by Anti-Jacob in Jacob's form. Other than in the Kate flashback (in which he's wearing a blue plaid shirt), he wears a dark or black suit in all of them. But since none of these people knew Jacob, it would seem to be a useless ploy. However, in touching them, he may have somehow 'read' them to see which one of these people he could later exploit for his loophole.
Of course, it could very well have been Anti-Jacob in the cabin, which begs the questions: did he really take Christian's form, and did he do it each time we saw him? After all, if he was bound into the cabin, then he couldn't have taken Christian's form in "White Rabbit", where he seemed to lure Jack of a cliff (where he was saved by Locke). He also couldn't have taken the form of Yemi. And if Anti-Jacob is Smokey (which I'm not convinced of, but many people are), then what good does it do to confine him in the cabin if his smokey form can wander fairly freely about the Island, taking the form of dead people?
So the questions are who was in the cabin, who put him there, and how long was he confined there? I guess I have eight months to rewatch all my DVDs and try to figure things out.