I emailed them a few hours ago actually (looking for the same info) and they do offer PAYG. The risk you take is it 'selling out' if you do PAYG since they won't let you reserve space for that.
"Greetings from sunny Cozumel!
For the Pay as You Option we offer free entrance and you will only pay for your consumption.
The pay as you go section offers chairs and tables with umbrellas, beach loungers, a small swimming pool, restrooms, showers and free WiFi.
We do not accept reservations in advance for this section, as it may not even be available due to the many all inclusive reservations that we have to honor.
Furthermore, we do not mix our Pay as You Go customers with our All Inclusive guests.
Please contact us early in the morning on your day of arrival in Cozumel to see if the Pay As You Go section is even available.
We hope to have the pleasure of serving you in our beautiful Beach Club."