Share iPhone 4G connection over an ethernet adapter?
It will work if you connect the iPhone via usb to a PC or Mac and then forward the connection over ethernet to a wifi router.


  This would work because iOS allows for hotspotting over USB. from there, you can use the sharing preferences on Mac to share internet, you may share the connection to any available interface, which includes wifi/usb to ethernet or any other interface that may be connected. 


With a wifi router, you would be able to access both wired and wirelessly what is on the network. The connection would come from the iPhone, go to the computer, then travel to the router; where a NAT would be created, and multiple devices connected to the wifi router would allow for communication between the wired and wireless devices. 

A note: your Mac and iPhone will not connect to the network because they are supplying the internet connection. Another device would be needed.

See Screenshot below: