To monitor an Amazon RDS instance using SQL Diagnostic Manager, you have to create a SQL Server user on the instance with the following minimum permissions:
Server Roles:
public, processadmin, setupadmin
Databases:
public on TempDB
sysadmin server role equivalent privileges for monitored databases
Securables:
Server Object: Connect SQL, Create any database, Alter any login, Alter any linked server, Alter any connection, Alter trace, Administer bulk operations, View any database, View any definition, View server state, Alter server state, Create server role, and Alter any server role.