All the cars use the Formula E chassis. They all use the same battery, which has less power than my dual-motor Model 3. The only part they can develop is the powertrain, which no one can see. Visually, all the cars will look the same. This is not F1 where a Ferrari is distinctively a Ferrari. A front-running Audisport, looks just like a back marker Nio.
It'd be far better for Tesla to run a bespoke car at LeMans, than in Formula E. That could be a car, distinctively shaped like a Tesla, presumably in the GT class, and they could learn something about cooling the battery that could trickle down to use in their regular vehicles.