In the case of checkboxes, no 'partial credit' is given. You must select all the options that are marked as 'correct' in the Quiz Score Answer Key for the question to be considered correct.
Show/Hide questions will be counted even if they are never seen, as long as they are marked in the Answer Key of the Quiz Score action.
However, not all questions in the survey must be part of the Answer Key. Any question that does not have a correct answer selected in the Answer Key will automatically be excluded from scoring.