No. It has never been actually tested for COVID-19. The only information they have is correlation. South Korea had some success with it, there were multiple treatments given at once. Also the recovery time has been anywhere from 4 days to 14 days without it, so it is really hard to determine how effective it really is. But since it doesn't seem to harm patients, every doctor who has access to it will use it. That means there is (and will always be) a shortage.

And since it will not prevent COVID-19, there is no need for pilots to use it. If they are sick, they shouldn't be at work and Delta does not really care if it takes you 14 days to recover without hydroxychloroquine or 10 days to recover with it. Right now we have lots of pilots, so there really isn't a need for Delta to reduce the amount of pilots on sick leave.

But let's imagine that there is a drug that is actually proven effective. Contrary to what many on here think, airline pilots are on the bottom of the list of people who will get access to it. It would be reserved for patients in serious condition and/or medical staff.