Today in Asana a project may be public or private.
If private the project (understood as list of tasks!) can’t be seen by not members!
Many times I’ve this situation but I have some tasks that have collaborator that aren’t member of the project.
That users can see the tasks (with or without edit right) but can’t see a list of the task of this project they are following.
My suggestion: can you evaluate a solution to permit at the users not in the project but that follow many task of the projects, to see that tasks in a list?