I used to use Morton Kosher salt, but I switched over for two reasons: even if the anti-caking agent is OK to eat, I'd just rather have my salt contain salt, and when I make pickles the anti-caking agent seems to make for a cloudy brine, where the straight sodium chloride doesn't. I didn't notice any difference in the many cheeses I made between Morton and Diamond Crystal, but I did notice it last summer pickling, so I switched.
It may be my imagination, but DC seems to dissolve more quickly when I make brine.