Your name is scrubbed from the viewer list. However, if they are actively watching the viewer list refresh, they might see your name appear and then vanish. Also, blocking someone removes them as a friend, so you will have to re-add them (which sends a notification).
By default, Facebook is a "glass house." When you view a Story, your name appears in the viewer list immediately. But is there a legitimate way to bypass this? view facebook stories anonymously
: You can create a secondary Facebook account with a different email address and use it to view stories anonymously. However, be aware that Facebook's terms of service prohibit creating fake accounts. Your name is scrubbed from the viewer list