My understanding of public surveys is that the results can be hidden from view in both web designer and connect by following the steps on the following pages:
If these settings are applied then the layer can be searched for and loaded into a web map but the features will not be visible and the attribute table cannot be loaded (message of Error accessing data).
What can be seen is the domains of fields which have set values when accessing through the filter tool and choosing unique. This seems like a slight loophole as it is therefore possible to get an idea of what is in the dataset and domain values could theoretically contain sensitive information.
When trying to populate unique values for fields without set values the message 'too many unique values to display' is shown. This does not explicitly say that data is not accessible (I felt the need to go and test this on a field with a single value to make sure it didn't populate the unique list) and it might inspire more confidence if messages shown when trying to access data in these secured layers stated more directly that the results are blocked, and didn't show domain values.