Is special equipment required to perform high-voltage line inspections?
I work in this area and, to my knowledge, I never heard about any special aid to help the pilot. They know precisely which are the wind speed limitations to do the work safely, the rest is basically skill.

What they do install in helicopters, is the so called Wire Strike Protection System (WSPS), which should cut the cable if the helicopter strikes it, avoiding damages on the main rotor (see the picture https://upload.wikimedia.org/wikipedia/commons/b/bf/Ntsp-oh58-N170FR-070205-01cr.jpg that Bell has two WSPS, one over the cabin another underneath the avionics bay). But this is more important on power line inspection, which is made at around 60-80 km/h with cameras and LiDARs. When the helicopter is hovering by the cables this doesn't bring much aid.

But this is a risky job anyway and if you search, you will find plenty of accidents which happened with helicopters and power lines.