Yes I have used RAC as well. It can be achieved via both Type 4 and Type 2 Oracle drivers.
1. Under WebLogic there is a concept of Multipool, which is like a pool of connection pool. You configure it either as load-balanced or as high-available pool. Under this option you can use Type 4 Oracle Thin Driver. If you dont want to configure multi-pool then you can use Type 2 OCI driver.
2. Under WebSphere 6.x and beyond the support for RAC can be achieved as follows:
(a) Configure one connection pool but use Type 2 Oracle OCI driver. The connection
string for the OCI driver (either under WebSphere or in TNSNAMES.ora) contains the information about both the RAC nodes and it will handle transparent application fail-over (TAF). To be able to use OCI driver from WebSphere machines, you will need to install Oracle client libraries on them. This client install is not needed in case of Type 4
JDBC drivers.
(b) Configure one connection pool but use Type 4 Oracle JDBC driver. The custom property of database servers will need to be configured in this case. The only issue here is that it works in high-availability mode. So all requests will go to first database node. When the first node fails it will go to the first server listed in the failover property and so on.
I think using OCI driver is a better option for effectively using all the RAC nodes.