Sure, if we are talking low power and fixed outputs.
But Tesla Superchargers provide variable output power up to 145kW, any system close to that much energy is going to have self-monitoring functionality as a safety precaution alone.
Can I prove it? Nope, I don't work for Tesla and don't have the time to research the build permits.
The Supercharger can measure current output directly along with voltage at its terminals. What it can't measure directly (unless there are remote sense wires which does not look like the case based on internal photos) is the voltage at the vehicle/ pack. Unless the vehicle reports its internal voltage sense value back specifically for this purpose, the Supercharger is going to bill based on gross power delivered.
Time of use could vary based on time start/end triggers, display rounding, and such.