Tesla's perspective
Obviously Tesla gets to sell some cars, but the real gains won't come in the direct sales to Hertz; not at their current numbers anyway. What Tesla has is a great product too many people haven't experienced first hand. And there is compelling evidence to support the idea that Tesla rentals will drive additional Model S sales.
In its Q1 2013 conference call, Tesla noted conversions after test drives were in the region of 25% -- a very positive number for an automotive test drive. Now, some of this can be explained by the fact that the group of people test driving the Model S are also the ones most in-the-know and enthusiastic about Tesla. But based on reviews of the Model S from a performance and driving aspect, it's a top-notch car and much of the credit for those test drive conversions is due to the quality of the Model S.
For people otherwise not interested in a Model S, or those interested but who don't have the time to test drive one, renting a Model S could provide an ideal test before buying one. Additionally, even those who won't cough up the $500 a day to rent a Model S at least get to see one in the Hertz rental lot. To those who are aware of the car, it will provide a real-life look and reminder. And for those unaware of Tesla or the Model S, it could push them to research the car and learn more about it.