Coming down Pikes Peak riding the brake pedal most of the way, in D, like a dumb tourist, in my Volt, when I stopped at the Park Ranger Safety station where they read your brake disc temps, the front disc was 75°F on a 65° day. The backs where at ambient. That was the fastest charge the Volt battery ever got!... In normal circumstances, you don't get any braking force on the rear wheels until regen has been tapped out. (I don't know that this is true, but I'll accept it as true for the sake of argument). What happens when you hit some ice and traction control cuts in? ...
As for braking, of any sort, on gravel or raining streets, these cars have an amazing Stability Control System. I'm pretty sure it applies individual brakes to save your bacon.
At least that has been my experience while flogging the 2 GM EV's that I have owned.