Hi Jarvo,
No, that is incorrect. Vendors can have multiple roles, such as “Vendor” and “Customer” or “Whatever”. But if you add a “Premium Vendor” role that will not work for vendors being able to access the Vendor Dashboard at all. Only the “Vendor” role will work for that.
This is something we’d like to write into Pro one of these days soon, it’s just on a long list of many other features we are developing for it. In time, yes, just not quite yet.
If you’re killer with PHP and wanted to fork WC Vendors on GitHub and then make the change so it allows multiple roles you are most certainly welcome to do so, and send it back to us as a pull request. If this paragraph doesn’t make sense, don’t worry, just pretend I didn’t write it. 🙂
Cheers
Ben