Well,
If you intend to have wordpress.com as your webpage or something, I dont think its a problem. Just you can't connect your MySQL thing so there will be no Control Panel, Forum, etc.
If you already bought a domain, you can use it to Asura Hosting's VPS
Btw, the "require an existed domain or sub-domain" in Asura Hosting billing can be changed later, so take your time.
Goodluck!