But it's not gravity fed, so no hydraulic head, or more accurately a hydraulic head that works in our favor. As with any other carburetor-fed generator that isn't gravity fed (the one on my RV comes immediately to mind), you bolt a small electric fuel pump inline on the generator by the carburetor so the pressurized line is immobile and only a few inches long. If I'm especially paranoid, then I make a hard line, but I'll probably use a reinforced rubber hose. The one on my RV has been working without leaks for over 20 years. If there is a breach before the pump, then it drains back to the tank due to the hydraulic head. If there is a breach after the pump, then you stop the leak the same way any other car on track stops the leak, with the kill switch.
All fuel hoses external to the car, or running inside it, would have to be run in conduit, so no leaks mid-line would be a problem, and fuel dripping on the roof is handled the same way as any other situation where fluid leakage could be a problem. I'd put an engine diaper pad under it, or just use a drip tray with a drain tube. Maybe a combination of both, although the pad would not be viable in the rain, but rain doesn't drip from the roof on to the driver, either, it runs down the rain gutter (80's cars still had rain gutters) out the back, which kind of makes my point. I'm not sure we even want to drive that car in the rain, the handling is exciting enough on dry pavement, and high voltage. None of these things in any way invalidates an unbroken sheet of metal as a firewall or changes the reasoning behind the rules.
As I said before, the generator on the roof will probably not be deemed track worthy, but not because of fuel. You have to ask what happens if the car gets upside down? It will either break away and fly off in some direction as a 200 pound projectile (most likely scenario) or get mashed through the sheet metal of the roof into the cockpit, where it would be an unwelcome intrusion, possibly damaging our large bust of Nicola Tesla, which took me over 24 hours to 3D print and melted the paint off of one of my servo motors. I don't want to have to print that thing again. Racing with it up there would require an exo-cage around it, which, while pretty damn cool, probably isn't going to happen.
Everybody grab your brooms, it's shenanigans!