Circling back to this thread to share my recent experience.

I made my reservation through Priceline with Hertz (via Autoslash) since they ended up being cheaper than Avis. Upon arrival at the Hertz counter in Cancun Airport the agent confirmed that my reservation already included liability insurance. He did explain that there was an option to purchase supplemental liability insurance which would significantly increase the amount of coverage that I had. The difference in rate was quite substantial though, it would have increased the cost of the 5-day rental from around $95 to $235. I declined.

As for the Collision coverage (CDW/LDW etc.), The agent had no problems with me using my CSR for coverage and he did not ask to see any sort of proof of coverage (i.e. Chase benefits booklet etc.)

The return facility was a bit of a zoo but they honored the "Hertz Valet" benefit due to my President’s Circle status - "Take advantage of our terminal drive-back service at participating locations up to four times a year as a President’s Circle member."