What amazed me, when they were placing the control head on, and the oil was gushing everywhere blinding the cameras, the ROVs were still perfectly able to remain on station. Maybe they also have some kind of sonar imaging or other stabilization method?
Regarding what you said about "hardened electronics":
I'm not sure if there is a lot of electromagnetic wave activity around such intense radiation (if so, I always wondered why they bothered to make steam instead of harnessing the radiation to make power) or if the radiation actually damages the chips etc by changing their atomic structure.
It's pretty likely that "hardening" would probably entail quite a bit of lead shielding in the form of cases for the controls, and maybe the cable too.
If cables are not needed, that would make life a lot simpler for the engineers.