Unknownreported this bug
Summary
Right now the Hide mechanic page does not give any indication of how one would go about manually unhiding a player after the mechanic has been applied. After asking in the support Discord, it appears that the ShowEntity mechanic is the proper way to do this, but it would be difficult to know that these two mechanics are related because they do not directly reference one-another. I think a link should be added to each mechanic's respective page letting users know that they are connected.
On Hide page: "Reveal hidden entities using the showEntity mechanic."
On ShowEntity page: "Reveals entities hidden with the hide mechanic."