There is no reliability problem with diesel engines. Most of the components on semi truck engines have a B50 rating of 750k miles or more. (B50 is a statistic on when 50% of the components would require a major repair, similar to MTBF on computer equipment) And diesels aren't that complex, until you start incorporating computer systems.
And you wouldn't drop a genset on an electric truck. That would be ridiculous. What you would create is a serial hybrid. It would have just enough battery to boost the available power for accelerating and steep grades. The diesel engine would produce enough power to drive the electric motors at highway cruise speeds. So the weight you gain with the diesel engine, generator, and fuel, you lose by leaving some of those heavy batteries behind. Diesel hybrids need to use some of the decades of experience of the train industry.
As far as safety is concerned, you'd have the worst of both worlds. BEVs are actually more dangerous that diesel fuel. Between battery charging, dangers from damaged batteries, and hazards to emergency service crews. Diesel, OTOH, is a known component and difficult (compared to gasoline) to ignite.
Some issues I see with the Tesla truck are that there appears to be no sleeper. So no team drive and the driver has to end their shift at some kind of facility. 60 mph cruise speed is too slow for the United States. 65 or 70 will be required, or you'll lose all your drivers. (drivers get paid by the mile) And it's going to need more than a 500 mile range. 10hrs x 70mph puts you at 700 miles minimum. I'm also curious how they are going to handle the un-sprung weight of having a motor at each wheel.