When the dismiss and take no action is selected the user no longer appears in the exception list and they are not assigned to the program - the user still appears in the audience though.
There is a problem if the dismiss is selected in error as there is no record of the users who have been dismissed and they still appear in the audience. To prevent this would it be possible to list the dismissed people in the exception report with an opportunity to undismiss them from the program. The description Dismiss and take no action could also be made a bit stronger as some action is taken - the users is not enrolled in the program (and assigned required learning).