@maxharrison Welcome to the Rockstor forum.
I’m linking to you other post (2 hours ago) which is essentially the same question:
Have you read the Plex Server Rock-on in the official docs? And the generic Rock-ons (Docker Plugins) sections. It covers an example of using a specific user for a specific Rock-on and how to minimise the use to just that user, a ‘plex’ user in that case. It also covers how to find out a users uid and gid and how to setup the share appropriately. All with pics of the relevant UI components.
As for the shared Rock-ons-root you can leave that at the default permissions.
Hopefully that should help to clarify things. Best to use specific users for specific Rock-ons where the Rock-on allows for this. And if you need to share read write access between rock-ons then use the group and ensure the users are members of the relevant group.