This has a happy ending! From reading and searching, I discovered the plugin called "Virtual" which seems to be exactly there for this purpose. This forum reply will also help anyone looking for this functionality in the future. Virtual allows you to create virtual switches (and other devices) which can then be added as responders to scenes. Turn on a scene and the virtual switch turns on too, and same for off. Then you can use the virtual device in a IF statement just like an actual device. Because the device only exists as a responder for the scene, no need to "guess" the status of several devices as suggested earlier.
Having this capability helps maintain the optimum failure mode for an Insteon setup, since Insteon is peer to peer. So if the eisy/PLM/whatever ever fails, the generic scene will still function, and only the additional functionality provided by the eisy will be lost. This is different than relying on eisy to launch the scene just because you also want added functionality in a program.
