Diaper rash cream did absolutely ZERO to help me with my itching, but that doesn't mean it won't work for others. The only cream that helped me with my itching is made by CeraVe and is their Itch Relief Moisturizing Cream formula.
As far as the concept of chelation for treating GD goes, my theory on that is that heavy metals in the body may be the cause of the disease for only some people, and those are the ones for which the cilantro works, about 50% as @gardeningjunkie estimates. Personally, I speculate that damaged skin from overexposure to the sun may also be a cause of GD, particularly in my case. This is total speculation on my part, but I have seen others mention this as a possibility as well. If this is an actual possible cause of GD, then I see no reason why taking cilantro would be of much benefit for these people's GD other than the fact that it has some beneficial nutrients, thus the approximately 50% of people with GD that it doesn't help. There appear to be no easy, one-size-fits-all answers with this disease, so we all just keep experimenting hoping to hit on something that at least works for some of us. Best of luck!