I read that post, as well as the one that was linked at the beginning... and personally don't have a problem with my piticular brand of Salt comming in a plastic 5-gallon container.
Sure... anything is possible, and I'm sure there are some who have developed a problem when using plastic containers to store one of their Reef animals in. How much of those problems can I attribute directly to a Salt-brand 5-gallon bucket causing??? Without intense testing on that piticular bucket, I hesitate in guessing.
For me, I don't feel there is any concern with those 5-gallon buckets, but that is "for me", and "on my system". It is what WE feel is best for our specific tanks, situations, and conditions. As long as we are trying to do the best we can for the animals in our care, that is all that can be asked.