I don't know how much Corexit masks the smell, but workers who have been close to heavy concentrations of the spraying report that it reeks like heavy ammonia and the primary ingredient in Corexit is indeed described as having a smell much like ammonia. Ammonia masks odors. Just another way BP has used that damn dispersant to cover up their crimes and liabilities.
I would love to see the head of BP get his family together and let one of us catch some fish in the polluted waters and serve it up to them. And then monitor them to make sure there was no stomach pumping going on after their meal.