Doesn't sound like your friend is asking about frequency dependent charging... just if things are ok when major events happen on the system. There are MW/Hz values for each of the three interconnections in the continental US (East/West/Texas) that while I probably can't show here, are pretty large. Like losing multiple very large power plant large. Usually it's expressed in a tenth of a Hertz. In other words, if we're down to 58 Hz, unless Texas is having serious issues, chances are thousands of grid operators are not having a good day.
Again, the frequency band is generally 59.95 to 60.05 Hz. Tripping of generators at say 57 Hz is due to the vibrations/resonances found at those speeds in steam turbines. (Not sure about combustion turbines/jets but I would think not) I know water turbines have essentially no reason to trip at low frequency and in one case a certain utility islanded in the 1950s and "survived" with some load at something ridiculously low like 53 Hz.
For the stations, I have not heard anything about incorporating under-frequency load shedding directly into them. I have heard about cold load pickup randomization where the station will randomly add a few seconds to a minute or two to the time that the station allows the car to resume charging after power is restored. Honestly, reducing cold load pickup is probably the best we could ask for. Incorporating underfrequency load shedding is going to be expensive in a stations' design and since the utility is going to have more accurate and regularly tested equipment, the utilities' relays are what should be relied upon for that purpose.
For the cars: the lower the grid frequency the higher the ripple current that needs filtering before the dc output of the charger. However, since we're in a global market, I believe that the chargers are built to handle worse case on a 50 Hz grid, probably down to 47 Hz. Thus, when we talk about 57-63 Hz, the ripple current is still lower than spec, and the car probably doesn't care. I only mentioned Tesla previously because I believe they measured and acted upon the grid frequency, not that their chargers couldn't handle the variation.
I talked a lot about grid stabilization, storage, and where I think V2G plays a role in a presentation I gave to the Silicon Valley EAA in March this year. You can watch it here: https://youtu.be/3K8bQ6krsSE?t=17m30s
If you send me a PM with you or your friend's email, I could send you the slides. To sum it up though: I think managing power flows and load demand are way more
financially desirable than frequency regulation.