My comment and assumption comes from a personal experience...
My sisters mother-in-law is allergic to shell fish and had a reaction at a family reunion several years ago...It was at a time where, in our area, sea salt was the all new popular health craze, and sea salt was used by alot of us in our recipes for our "dishes to pass".
Since no shell fish was served the doctor's at the hospital made the connection (quite possibly wrongly) between the sea salt and the reaction.
She has also had two more occasions of incident where the only common denominator was the sea salt.
Now it could have been simple over exposure due to the sea salts wide use and with normal use and under normal circumstances it might not (have) happen(ed); it could have been something all together different that triggered her allergy, but she (as well as the rest of the family) decided "better safe than sorry" and simply avoid it's use.
Now, I'm certainly not trying to dissuade the use of sea salt, raise false alarms or spread untrue rumors however, knowing the large numbers of folks that eat my BBQ I don't know intimately, and in assuming that's true for many of our forum members, I was simply sharing in hopes of sparing any others from that harrowing experience.
There are others here far more knowledgeable and experienced than I and I've come to respect that knowledge and expertise far too much to tarnisg this forums image with falsehoods...
If those of you who are very much more informed than I decide there's simply not enough evidence to support my assumption, I'd HAPPILY rescind my friendly warning.
As I said, I certainly don't want to be responsible for the spread of falsehoods...