Years ago we developed a solution to integrate Apex with Oracle's eBusiness suite.
It worked fine on 11i, and we came with a jsp solution for some of our initial R12 customers.
We had sometimes the "Apex is not supported by Oracle for the EBusiness Suite" discussion.
On the Apex site you can now read the "official" white paper how to integrate Apex on Apps. You should be on a recent 12.1.3, and it requires some patching.
The paper is introduced on David Peake's blog, Apex product manager.
I will blog how it works out, the next time we gonna use the official integrator.