Re: Flash
It all depends on the firmware in the Flash controller. I suspect that any faulty areas will be marked as unreadable, but would doubt that it'd go much beyond that. For example, performing an erase on a bad area WOULD wipe any stored info permanently, but I don't think any but the most paranoid, security-specific FW would go that extra yard.
If you run a zeroing utility on a spinning rust HDD, will it attempt to overwrite excluded bad blocks as well as the 'good' data / directories?