Yes, you require a separate Oracle license for the DR/Standby database. Note, this Oracle license should be the same license metric as the primary database. This means that if you license the Oracle primary database per CPU, then the Oracle standby database must also be licensed per CPU (although it does not have to be the same number of CPU). Or if the primary database is licensed per user then the standby database must also be licensed per user. If we go for a Standard Edition processor-based licensing option this allows us to have up to 2 processor sockets in total per database.
For your Oracle licensing you will require a separate Oracle Standard Edition license for the standby database which is also processor-based.
If you are using bare metal servers in the cloud then licensing is essentially the same as on-premise. If you are using OCI base database service that includes both the hardware and oracle license, you can create your database with a configurable number of oCPU. For Oracle Standard Edition you can choose 0-8 oCPU.
For your Oracle License you will need to license each database, the primary and each of the standby databases.
There are two main options depending on your Oracle version. For Oracle Standard Edition you can create a simple standby using scripts or create a more comprehensive solution using third party solution like Dbvisit StandbyMP. For Oracle Enterprise Edition you can use the included Oracle Data Guard. If you would like to use that for reporting purposes, similar to Dbvisit's snapshot functionality, then you will need to purchase Oracle Active Data Guard.
StandbyMP is licensed by database, not oCPU, CPU socket, or user. This means you will need 1 license for each database. For example, for the most common Primary database protected by a single Standby Database you will need 1 StandbyMP license for the primary and 1 StandbyMP license for the standby, for a total of 2 StandbyMP licenses.
A second example is a single primary database protected by 3 standby databases, perhaps in different geographies and at different delays. In this case you would need your 4 StandbyMP licenses, one of the primary and three for each of the standby databases.
You can check the price of a basic StandbyMP solution including one primary and one standby database here on our pricing configurator. We offer individualised pricing for larger environments or customers requiring multiple standby databases.