Well, I think the cam has a place in diagnosis... Even with 'hit or miss' issues, the reality is it can go where no scope can reach (no matter which directon they take)
Also, inflamation is typically blotchy in crohns outbreaks, esp. in the upper GI tract. Even if it missed one or more areas, the moment it catches a pic of any inflamation where otherwise a doc couldn't scope it, it confirms the diagnosis.
IF it wasn't considered an 'effective' tool, it wouldn't be used. Why? Insurance providers who'd kick at the cost... I mean, an individual might pay for it without questioning whether it was worthwhile or not; as most accept a dr's say so. But insurance companies... No, those bean counters wouldn't stand for it, and they have their own 'doctors' ready to 'testify' that a procedure is too useless, or impractical, or not applicable, or experimental.. for it to be 'worth' covering.
Anyway... if a doc suggests (OK's) a laxative, esp. a mild, overnite laxative, it's probably a safe idea to take it.. Just might ease more than ones mind with it.