If you let someone borrow your car, then the insurance follows the car.
If you rent it, it's a commercial transaction and it may not be
covered. You should probably get a copy of their insurance card, and
request that they up their coverage to at least $1,000,000.
I'd like to rent my DMC too but haven't figured out the liability issue
yet and haven't gotten around to talking to my agent. In my state, the
law immunizes licensed car retnal companies from civil liability caused
by their renters, but obviously that doesn't cover me.