Since Hertz doesn't charge up front for the rental, I completed the booking online to see what would happen. I used 3750 points for the one week rental of a Large Luxury Sedan. After completing the booking, a reduction was applied as a "Promotional Discount" of $390.00 (i.e. the full amount of the Base Rate).
The Taxes, which are clearly linked to the Base Rate, remained unchanged.
The Airport Concession Fee, which appears to be tied to the Base Rate, was removed from the final bill.
The Vehicle Licensing Fee Recovery, which appears to be a flat rate of $4.00/day (for the location selected), was not reduced.
The AP CONTRACT FEE, which appears to be a flat rate of $6.00/day (for the location selected), was not reduced.
I find it odd that the fee tied to the Base Rate was reduced, but the Taxes were not. I also find it interesting that the only change to out-of-pocket costs for the reward redemption is in Taxes, which suggests to me that it is worthwhile to book at the highest vehicle class available (within the standard reward tier).
Thank you to everyone that took the time to respond in comments and/or answers.