When you visit a padlet page created by another Padlet user, that page may collect more information than we do and may provide information to third parties that we have no relationship with. We request you use discretion when sharing personal information on padlet pages created by other users.
How? Is this because embedded resources (YouTube, etc.) will send information to their host sites? Is this process automatic on displaying the padlet or is it something that would happen on clicking the resource?
A partial answer below addresses this - this does appear to create engagement trackable through those original sites. "You may access Third Party Services through the Service, for example by watching a YouTube video on a padlet. "