Broccoli has properties that make it a killer of E-Coli, and that is why it can help with Crohn's. The MAP bacteria secretes Mannose which in turn feeds E-Coli in the intestines. The Mannose is speculated by some to possibly mask the MAP bacteria from the immune system.
If E-Coli is causing trouble, then given some time Broccoli may help. If it is the MAP bacteria causing problems, it is not going to really help much with that.
Of course there are also other theories on what causes Crohn's symptoms, but I do subscribe to the above theory.
Dan