Since wpVoucherPro mostly hooks up to native WordPress functions the short answer should be yes. We give our very best to ensure our product uses the latest “best way practices” for wordpress plugin development.
Short and simple: 1 domain / subdomain = 1 license key. You can sell your license key at any time. Please note: If you sell your wpVoucherPro license, make sure you give the customer access to your wpvoucherpro.com account.