As part of my new role on Connect managing the Archiving and eDiscovery Community (and Partner Community) I've just learned about a new set of documents created by the EV Content Council that you may find helpful:
You can find the necessary information on the various accounts and users that are involved in an Enterprise Vault environment, as well as the permissions required by each.
Enterprise Vault Accounts and Permissions
Compliance Accelerator and Discovery Accelerator Accounts and Permissions
As always, if you have any feedback on the documents or suggestions please do leave a comment.