It is possible to manage multiple domains from a single account.  When multiple domains are linked to the same account you will see a "down arrow" next to the domain name in the upper right corner of the control panel.  Clicking on the "down arrow" will display a list of domains that you can toggle between and manage.

How to add multiple domains to a single account:

• Order your first domain using the normal order form to set up your account.
• For the rest of your domains, use the alternate order form to add the domain to your existing account.

There is also a button in the SpamHero control panel that goes to the alternate order form for adding additional domains to your account.