Is it possible to serve a hosted FileMaker file from a copy of FileMaker Server running on a Mac, over usb only, to an iOS device running FileMaker Go? That means without WiFI, without 3G, without 4G, without LTE, no radio at all, radio silence. USB cable connection only. Not copying files, no iTunes, no third party sync solutions, but live service from FM Server to an iOS device over USB.  Thanks for any insight!

No, but even if it was, it is not recommended.

That would equal to serve from an external device.

However, I have seen devices to plugin to an iOS device, with a RJ45 ethernet cable. This should in theory put your iOS device on a cabled internet connection. If that is working, you should, in theory be able to turn off all radio on the iOS. I have such plugin device, but was never able to make it work.

I found these solutions online, I'm going to go buy the parts and see if this works, will let you all know!
http://www.gottabemobile.com/2014/08/28/how-to-connect-an-ipad-to-ethernet/

and

http://9to5mac.com/2014/01/10/video-connect-your-ipad-to-the-internet-via-ethernet-cable-with-this-easy-hack/

No, but even if it was, it is not recommended.

That would equal to serve from an external device.

However, I have seen devices to plugin to an iOS device, with a RJ45 ethernet cable. This should in theory put your iOS device on a cabled internet connection. If that is working, you should, in theory be able to turn off all radio on the iOS. I have such plugin device, but was never able to make it work.

unfortunately no iOS device I know of has a J45 connection.

Folks good news, the answer is 100% YES, using the assortment of adapters mentioned in the videos listed. 

It is in-fact possible to access a filemaker hosted database in the manner described:

iPhone (6 plus in my case) > Apple Lightning-to-USB adapter > Powered USB Hub > Apple USB-to-Ethernet adapter > ethernet switch or router > ethernet on Macintosh running FileMaker Server. 

As the videos state, you must use a powered USB hub, to supply the additional current required to run the Apple USB-to-Ethernet adapter. Also, as the videos state, sometimes it works, sometimes it doesn't. I have been able to discern a pattern to when it does work and does not work. You will in-fact get an error message the first time you make all of the connections, stating that the "Apple USB-to-Ethernet adapter is not supported". The "trick" is this: Disable all radio functions, plug everything in, restart the iPhone, the very instant you are able to open Safari, do so and attempt to load any web page BEFORE the adapter warning comes up. In my case, I have about two seconds. If you manage to do this in time, the web page WILL load, then the warning will then appear as usual. You can tap away the warning, and continue to browse web pages over this connection. Close Safari, and you're good to go. Open FileMaker GO, you should see your host under Hosts. However, you must type in your file name to open the file, something may be blocked in my case. Once in, the connection is rock solid until you disconnect something, then you have to begin the process all over again to re-establish a connection.
So that's it, FileMaker GO access over ethernet. I welcome any "cleaner" solutions, though.