Most issuers (including Visa, Mastercard and Amex) do not allow automatically recurring payments with their prepaid credit cards.
This means that although you might be able to use a prepaid card for the first month, or first year, of your subscription, the next payment will not go through and your access to the classes will end.
However, it is possible to pay for EkhartYoga gift cards for yourself or friends with a prepaid credit card.