To undersand this I think you have to consider the total business model.

Basically to make money the renting company needs to be able to make more rental revenue during the period of ownership than the depreciation of the vehicle. Given dismal 2 year resale prices of the Taurus for example (which losses more than 50% of purchase price after 2 years of use) you can easily see why some imports in the fleet make sense.

There are few vehicles with 2 year depreciation worse than the Taurus given this it's fairly easy to imagine how Hertz can make more money in total having a fair number of GM vehicles in the fleet (given even a modest superior resale fraction).

As to the issue of whether Ford will sell Hertz, seems to me that the answer is obvious by their fleet actions. If Hertz has no value as an outlet for (Ford) vehicles which are not consumer viable, then it has no value at all to Ford. Given the increasing population of GM vehicles in the fleet, looks to me like a decision has already been made. Ford will attempt to sell Hertz.

Lihu'e 1k