Ultimately, even with the high performance of the Jaguar's embedded controller I am concerned about using a digital measuring system to measure 'brown outs' because the noise spikes are short and they could easily alias the conversion process. If you get a good shot of noise into the circuit and it's very brief you might not even know it was there.
I've worked on some integrated circuit design and there are a few ways to go about the idea of an internal reset and brownout detector and sometimes the nice clean digital approach isn't a great idea around motors.
In other robotics designs...for example the RB5X (circa the 1980s) they used to use 2 batteries. One for the control circuitry and one for the drive motors. Specifically because this meant the noise couldn't walk back to the control logic as long as you had some isolation. They used 'logic level relays' to operate those drive motors, so there was no physical connection between the motor battery and the logic battery.
In this case, we don't get many choices with the Jaguars because they steal their logic power from the same terminals that feed the H-bridge.
BTW, in case anyone here never heard of the RB5X robot:
Meet a blast from the past and a certain recent Pawn Star TV show episode....
http://www.rbrobotics.com/
http://www.rbrobotics.com/Specs/rb5x_specs.htm