We can host any domain name either registered with us or not.
You do not have to register your domain name with us. But having your domain name and web hosting account at the same provider will help you with many aspects in the long run. For example, we will be able to do the changes that might be required for your domain name.
If you would like to keep your domain name with another registrar, all you need will be to update the name servers of your domain name to have it hosted with us.