You may have an external consultant in your organization, who should see the survey results, but isn't eligible to participate in the survey itself. It is possible to set a flag against a user to prevent them from being sent any future surveys.
The observer can still perform survey configuration if they have been set up as an Administrator.
Use the checkbox on the Permissions section called Observer.
If a person is already invited to a survey, and then later made an observer, the person can still take that survey. However they won't be included in future surveys. You can see who has been made an Observer on the Participants page, by looking for the 'observer' label against their name.