You can hide the widget if the terms are NOT matched by using the exclamation point before the function, i.e.,
!is_tax('taxonomy_name', 'taxonomy_term')
If you need to hide it for multiple terms, in that second declaration (where it says 'taxonomy_term') you could put an array:
!is_tax('taxonomy_name', 'array('first_taxonomy_term','second_taxonomy_term','third_taxonomy_term')')