Thanks for the replies. As there is some uncertainty in the area of incidentals and Diamond benefits, I thought I'd look into the T&Cs.
Here is what they say concerning incidentals. This seems crystal clear to me. So, what explanation was given when incidental points were denied?
3. Hyatt Gold Passport members may receive Hyatt Gold Passport points on Eligible Incidental Charges, even when paying Ineligible Rates.
Regarding Diamond benefits, the T&Cs are not so clear. It does seem that if they were intending to exclude PL users, they would have used the term "Ineligible Rates" in this text, rather than exclusively referring to airline crew rates.
8. Platinum and Diamond members will not receive Platinum and Diamond benefits when paying an airline crew rate.