I decided against integrating E-Business Suite Open Interface into my APEX application as I didn't really need it at the moment.
Nevertheless I want to quickly give my view on it. Open Interface tables (OIT) seems to be the common use to do interfacing with EBS. It looks especially interesting when you have to load a lot of records into EBS. Open Interfaces do a lot more than the API calls, in fact they may do multiple API calls at once and they keep error records too. Many products in EBS have a number of OIT available.
If you google for Open Interface table (or just open interface ebs) you find a lot more info than I'm giving here.