You don't (typically) incur a debt to Disneyland, so legal tender doesn't apply. Disneyland can refuse to accept cash at the ticketing office, but if they let you in and billed you later, they'd have to. The concept of legal tender is specific to payment of debts.

If you did a credit card chargeback and Disneyland sued you for the new debt that caused, they'd have to accept cash as payment.