Python comes with a simple http server built in. If you have python installed (which is the case on both the OVM server and the OVMM host) you can start it with:
python -m SimpleHTTPServer
To make it easy for you, go to directory where the ISO file is located, start the http server and verify that you can see the file listed in a web browser. Then do the import in Oracle VM Manager.
In this case I copied the ISO file to OVM server (dom0) and started the http server there, and the URL for the import becomes as shown in the capture below (or use the IP address of the server where the ISO file is located and remember to use port 8000):
The name of the imported ISO is the same as the file name, rename to a say Oracle Linux 6 U5 and put in the origin of the file in description.