If you're just using project archives standard, and not mixing use of project archives with the server's view, then you should be 100% fine. This ID is the module id for each archive. This is so when you deploy a module, it can remember which module you're deploying.
Admittedly using an id like projectName:outputPath could have worked, but then any time hte package was changed, I'd have to refactor the id, or if the project was renamed, I'd have to refactor the id, and all of these things would lead to problems, specifically that if you had already deployed a project archives via the server's view, the OLD module would no longer be found (since hte module factory only has the new id) and, well, this is what we have now ;)
So if you're mixing use with the server's view to deploy your project archives, you should definitely have different id's for each archive