Just did an award night at the CP in Mexico City (World Trade Centre) and the tax was included in the award. I was not charged anything (other than the breakfast charge which I expected to pay). Note that there are two taxes applied to hotel stays in Mexico City, the 15% IVA and a "Lodging Tax" which appears to be another 2%. Neither showed on my award bill.
Do post about your experience at this property. I passed it the other day walking from the main square over to the park and it looked interesting...very convenient for tourist type things, and lots of restaurants in a relatively safe area.
The reservation confirmation wording you quote is boiler plate and often does not reflect the actual details.
I also used a BOGO Wkend 2nd Nt Ambassador certificate at the IC Presidente in Mexico City and there was no tax charged to me for the free second night, though that property has an odd "Hotel Fee" which was charged.