All archived posts and comments, whether deleted or not, were made publicly available by people who wrote them. That means they were put up for public consumption, which was known to the user, and archived by databases these tools fetch content from.
Simply put, this kind of archiving of Reddit content is legal. As long it was legally obtained by these tools, there shouldn't be any legal implications with viewing deleted Reddit posts and comments.
However, if an individual were to use deleted content to defame or blackmail another person, legal implications may arise.