The answer is sort of. You could already host an IPFS website on your own domain. The dedicated gateways can be thought of as a host that allows you to serve up any content you pin on Pinata. Rather than a single website, it is the place where you can pull any files you've pinned on your account.
And yes, you can have more than one domain on the Professional account. Each additional gateway is an extra $10/month FYI.