In addition to what Mark/Jeevan mentioned, I’d say that when most people buy the Oracle Apps adapter, they are not so much getting it because of the adapter itself but because of the Predefined Transaction services that you can get with the adapter.
The Predefined Transactions services are simply flow services that webMethods developed, which use the Oracle Apps adapter to perform some very common transactions on the different Oracle ERP modules, such as Financials, Human Resources, Order Management, etc.
If you tried to use the JDBC adapter to do all this, yes, you could get it done. HOWEVER, you would end up doing a lot of work that is already implemented.
#Integration-Server-and-ESB#Adapters-and-E-Standards#webMethods