Does each domain have its own IP address? If so, then you should be able to do this. You would start JBOss using:
run -b www.mydomain.com
or use the IP address instead. This binds the jboss app server to that IP address.
I do not know how to bind the Oracle 9i App Server to a particular address, you will have to read the 9i docs to figure that out.
Most likely, the "www.mydomain.com" port 80 is going to be used for Oracle9iAS because it is current running live. In that case, do I still need to do binding of OAS to "www.mydomain.com"?
If my other domain, which is "app.mydomain.com" has a different ip, then I can run this "app.mydomain.com" using port 80 as well? In this case, should it be run -b app.mydomain.com ?
If my other domain, which is "app.mydomain.com" does not have different ip, then I cant run it using port 80 OR I cant name my JbossAS as "app.mydomain.com"?
You cannot run it using port 80.