If you are referring to using Visa to pay for Joomdle's subscriptions (ie paying the Joomdle Team), then yes we only use Papal as Antonio has specified.
If you are referring to paying for courses on your site, the payment method (Visa, Amex, paypal, etc.) is abstracted from Joomdle as Joomdle works with the shopping cart (ie Hikashop, VM, etc.). The shopping cart will manage the payment gateway. For Visa payments, it will depend on the shopping cart payment plugins. For example Worldpay, Authorize.net, Paypal, CCBill, all support Visa. To be sure, you will need to check with your shopping card extension to see what payment plugins exist and if those gateways support Visa.
* For Hikashop
www.hikashop.com/support/documentation.html#hk5
* For VM
extensions.virtuemart.net/payments
