One thing to be aware of that I have read about is that when using the DNG Conveter method of checking hashes, if the file is really corrupt, DNG converter might not recognize it as a DNG file and therefore will not flag it as damaged. You have to count the # of dngs you have before and after running the conversion.
I have read that ImageVerifier automates this process: it will use DNG converter to verify DNGs without actually converting them. I haven't tried it, but it might be faster. I don't know whether IV will tell whether a DNG file is damaged beyond recognition.
IMO, the fact that LR does not have a way of automatically checking the DNGs hashes across your catalogue is a major fumble on Adobe's part. Actually, wait, they just had record profits this quarter. They must know something I don't know about making money.