Payonner is often used to send mass payments for affiliates/freelancers and offer a prepaid credit card but as payment gateway, like any other platform, you can integrate it with WHMCS with their API. But are there advantages to use Payoneer compare to some other gateway like 2checkout or stripe ?
Payoneer don't provide direct way to receive money. It is not a payment gateway. But 2Checkout and Stripe (the list will be long if I enumerate all Payoneer partners) provide payments gateway with WHMCS. So, you should go with them.
With PayPal also, you can receive money and withdraw it to your Payoneer account (must be in US).
I hired many freelancers and they asked me "can you pay me via Payoneer"... I answered "sorry mate I only use Paypal" and they replied back "I only can receive payment with Payoneer, because Paypal is not supported in my country.". I think many people are using Payoneer, it is better to have this option in whmcs.
Payoneer is a global online payment getaway. You can send or receive funds from Payoneer. However, you cannot use payoneer to sell products and services. Payoneer has over 100 partners, these companies send payment to their clients through pyoneer. Payoneer has not integrated buying and selling services and products just like paypal. If you want payoneer for WHMCS, you can get this service through third party services such as 2Checkout and Stripe. You can get payoneer membership through these services.