As an experiment after i got my Hopper 3 and 4K Joey, I disconnected the coax from my 4K Joey and plugged in the Ethernet on the 4K Joey to my home's Gigabit Ethernet LAN. After reseting the network, my 4K Joey found the Hopper 3, but even though the Default Gateway and DNS settings were correct, the 4K Joey did not think it had a connection to the Internet.
I decided to stop messing with the LAN and stick with the MoCA when I saw the bandwidth report on the Hopper 3 showing the throughput was 680 Mbps. If the 4K Joey was pulling that much data from the Hopper 3, no way I wanted that traffic on my Home LAN.
I believe the acceptable WiFi connection would be to put the WiFi USB on the Hopper. But as someone suggested, using the HIC to connect your Internet to the MoCA coax connections would probably be best.