Esri does not license Oracle deployments. It licenses ArcGIS for Server hosts. Enterprise geodatabases require an ArcGIS for Server license.
Back in the days when ArcSDE existed, the licensing was applied where the application server resided, but ArcSDE doesn't exist, and neither do application servers. You can run a fifty node Oracle RAC database, and it could still only require one ArcGIS for Server seat (probably ineffectively, but that's a technical issue), depending on how your ArcGIS Server site(s) is(are) configured. Since you did not address how your ArcGIS for Server sites and servers are deployed, there's no way to say how many seats of ArcGIS Server are required in your configuration.
The fact is, licensing is NOT a technical issue -- it's a contractual one, which is why I recommended you speak with the folks who know the most about contracting (who are not over-abundant here in the technical forums). Yes, the issue impacts technical deployment, but that just reinforces getting a proper understanding from the folks who are working with licensing on a regular basis (and presumably know what you have licensed to date).
The usual steps for ArcGIS for Server deployment are:
- Collect requirements
- Design an initial implementation
- Cost the implementation plan
- Redesign in light of costing (loop back to 3 until plan is most cost-effective)
- Execute the purchase
- Install and configure the implementation as per design
- Maintain the GIS deployment
This GeoNet forum is more about the nuts-and-bolts of steps 6 & 7, and only lightly addresses steps 1 & 2. The best way to understand steps 2-4 is to start by discussing the licensing model with your local Esri rep. They'll be able to give you an overview of how ArcGIS licensing works and some boilerplate Server designs from which to get started. If they can't answer technical questions, they'll have access to experts who can. Ed Services has a three-day class on System Architecture Design Strategies, and the Systems Integration team has a wiki site, but neither is going to address licensing differences between single-node and RAC deployment of enterprise geodatabases (because there aren't any).
- V