You are certain of this?
Well, can you imagine the outrage if someone wants to pay with cash, is asked "are you a guest of the resort?" They say yes, and are then told they can't. Then the guest next to them answers "no" to the same question, and is allowed to use cash?
What would prevent the resort guests from simply saying they are NOT a resort guest?
In order to gauge the success or failure of this "test", there has to be a control in place. The control is "no cash accepted anywhere within the test property." Otherwise, it's not really a test, it's an OPTION for resort guests to disclose their status and then comply with the no cash rule.
Obviously they are trying to determine the feasibility of going cashless at the resorts (at least). The only way to get accurate test results is to maintain the "no cash" policy for the duration of the test period.