Yes, Email Marketer Pro allows you to have seamless integration with your clients websites, so you can have subscribe and unsubscribe forms on your clients web sites, but still have the core Email Marketer Pro files on your web server.
To create forms you simply need to select Manage Forms from the control panel on the index page of Email Marketer Pro or from the text links in the top right of the application. Simply follow the steps for creating a form and when you have completed this copy and paste the HTML into your website where you want it.