Oracle Real Application Clusters (RAC) is a cluster database with a shared cache architecture that supports the transparent deployment of a single database across a pool of servers.  RAC is certified with both Oracle E-Business Suite Release 11i and 12.  We publish best-practices documentation for specific combinations of EBS + RAC versions.  For example, if you were planning on implementing RAC for EBS 12, you would use this documentation:

• Using Oracle 11g Release 2 Real Application Clusters with Oracle E-Business Suite Release 12 (Note 823587.1)
  

Many of the largest E-Business Suite users in the world run RAC today, including Oracle; see this Oracle R12 case study for details.

A number of customers have recently asked whether RAC One Node can be used with the E-Business Suite.  From the RAC website:

Oracle RAC One Node is a new option available with Oracle Database 11g Release 2. Oracle RAC One Node is a single instance of an Oracle RAC-enabled database running on one node in a cluster.