Refer to "Configuring the DB SPI after New Install and Upgrade" of DBSPI Install/Config Guide.
This topic contains pre-requisite for each RDBMS vendor that you are going to monitor. For example, for Oracle RDBMS , you can find information like what previleges needs to be given to the user. This user will be used in the dBSPI configuration for monitoring the database.
BTW, there is a tool to create Oracle User as well.