You can have your EJBs as clients to your corba service. Normally, you would like to get your idl file, generate stubs/skeletons using the idl compiler to java. I'm not sure if omniorb provides you with such a compiler, but there should be one(Visibroker provides an idl2java compiler for me). Place the generated stubs from the idl (which will be class files) alongwith the jar file which you deploy for your ejbs.
Start your naming server for omni orb, start your corba servers and then start the jboss with your EJB (Corba client) deployed in it...There shouldn't be an issue...