Is the a viewer for .iso files that our non illustrators can use?
There is a thumbnail viewer in the release of 7.1. It can be installed stand-alone and does not utilize a license. Limited, of course, because it is a thumbnail viewer.
To view files in ISO and CGM format can be used free software from PTC - Creo View Express 1.0: http://www.ptc.com/products/creo/view/express/
P.S. Here is a list of file types that can be opened in the Express version 1.0: