Question: Should the -R option work with a self service adjoin?
#adjoin <domain> -S -R <computer_role>
Answer: When using the -R option to add a system to a computer role, permissions to update AD are required. A self-service join uses the machine credentials to join the system which does not have rights to update AD, as it should. This is as designed.
To add a computer to a computer role during adjoin use Domain Admin account credentials when executing the command.
#adjoin <domain> -z <zone> -R <computer_role> -u <domain_admin>