The batteries (high energy capacitors in reality) are not normally near the fuel tank. If I recall the briefing correctly, the biggest chance of injury to an outside person is touching the car barehanded as the carbon fibre conducts electricity.
Talking to the teams at Silverstone, the risk of something happening to the energy store is highly unlikely, but like everything there is a possibility (like fuel spill/fire) The gloves are for the incident marshal to wear when isolating the car should it stop out on track. But on most circuits, a mechanic is only a short quad bike ride away should it be a bigger problem.
