Yes. Guests can see each other’s names and can interact with each other (tag each other, assign tasks to each other, etc.) only if they are the part of the same project, or the same team. I had a problem with that because I work with a lot of guests, so I created a team and invited all the guests in it, so they could cooperate with each other. The same effect can be achieved by putting them all in the same project, but I couldn’t do that, because I don’t want all of them to have access to all the tasks in the project.
Also, important note - if you add a guest as a collaborator to a task, he is not able to see which project that task belongs to - unless the guest in question is already part of the project.
I hope this wasn’t too confusing.