You can ruin the computer on any car when the polarity gets reversed, not only hybrids.

As for charging the 12V:
The good thing about the Toyo system (I don't know Honda's) is that it doesn't take much to start it (12V system). You could probably use your cell phone with the right connections.
The 12V battery is needed to start the computer & close up the relays to the traction battery, not much amperage needed for that. Once the relays are closed, the juice from the traction battery will start the car and charge the 12V battery.