I don't consider RDL's and GM's that similar. The big problem is lower back absolute strength and strength endurance really need to be on target for GM's as compared to RDL's as with RDL's you can basically think of it as the lever arm being shorter. The weight is closer in to your body. With GM's whatever weight you put on is compounded by the distance out from you center of mass it sits. If you are willing to go light and work up slowly then I'm not going to make a big huge deal out of it. But I wouldn't advise GM"s over RDL's to start because RDL's are a better exercise, imo, with which to learn proper hip extension. You also, should not be worrying about your hams....think about your glutes and using your hips. The hams will be there as a side effect.
But you are putting the apple cart before the horses. You need to think more about total core endurance, imo.
The idea of trying to use an exercise to buffer against what may go wrong makes sense on paper. But in the real world when something goes wrong it can be somewaht a chaotic situation. So in other words you focus on ONE aspect of what could go wrong you fail to prepare for a more general buffering. And that entails having the ENTIRE core as strong as possible to protect IN ALL DIRECTIONS. I would spend my time on that. Use exercises that help ensure that everything will go RIGHT. Whatever that may entail.
I could also add to that that doing something bad to prepare for something bad probably won't be a good idea in the long term, and maybe not even short term...so if you can't control your lower back, or you believe loaded lumbar flexion will protect you against loaded lumbar flexion you must also believe that crashing your car into a brick wall will protect you from that
As far as the vid I think your lower back rounded out too much at the bottom. Not the worst I ever saw but it should have remained set. Don't worry about going so low that you can't maintain the back. This should be nothing more that a violent extension of the hips while the core provides support. Do not think in terms of aribitray depth positions becasue guru X says to always go to parallel. The whole point is not to train your back to recover when it moves into flexion. The point is that your back SHOULD NOT move into flexion.