I think Blacksheep meant the traction control, not the rev limiter, as you couldn't turn the rev limiter on or off
And as far as I know the TC measures the speed from the unpowered wheels.
The difference beetween drive-shaft measured speed and unpowered wheels speed is used to calculate the amount of limiting (by cutting ignition or fuel - not sure what is used) needed to match the speed from the powered wheels to the unpowered wheels.
The percentage of slip in the setup, is the amount of wheel difference allowed without limiting the power output.