Hi @philrz and great question!
You’re correct in thinking that Zenhub Issues are scoped to a workspace. They won’t be visible to anybody outside of your organization. Workspaces are currently accessible across all organization members, so everybody should have access. If you want to collaborate on ZH issues across workspaces, you’re also able to import one workspace Zenhub issues into another via “Add issue sources” section on the Edit workspace page.
When bringing in Zenhub issues from other workspaces, they will behave in the same way as GitHub issues on the board, eg: you can setup automation via Workflows and you’ll be able to toggle these issues on / off via the repository filters.
More info can be found here