The answer is yes, you can process an adult website with sepa payments. However, there are some limitations that you need to be aware of.
First of all, the adult website needs to be a merchant account-backed site. This means that it is processed by a bank or payment processor. You can't use sepa payments on a site that uses an e-commerce solution like Shopify or Magento.
Second of all, you need to make sure that the payment processor will process the transactions with sepa payments as well.