It should not be necessary to defrag the filesystem normally, so I doubt any scheduled process does this. Also, IIRC the 722 uses xfs, so there will be no fscheck on reboot. The only potential way to make sure the bad blocks get weeded out is to reformat it, and depending on the formatting flags Dish uses, that might not fix the problem. You might have to do a low-level format of the drive while connected to a PC to map out any bad blocks. If you are going to do all that, you might as well just get a new HDD or receiver, depending on whether it is owned or leased, respectively. You'd just have to copy your recordings to an external USB drive first, so you don't lose anything else.
Marking the bad recording do not delete should prevent other recordings from experiencing the same problem in theory.
Ted