I doubt they could ever get hold of something like that. Even a FOIA request should not return personnel info such as discipline or medical records.

In the past, some majors (yes DAL) would ask for copies of your FITREPs but I don't think they still do that.

So I doubt they'd ever find out, unless maybe your references know about it.

But in this climate, checking that box isn't going to keep them from calling a mil pilot, or even delay it IMO. They'd appreciate the honesty frankly.

However... do you have a copy of the letter? They might want to see that, and if you don't have any records to document your explanation that might be a problem. I've known that kind of thing to hang people up in the past. I suspect it wouldn't just due to the hiring demand but something to consider.