Yes. All eeros can be connected together via Ethernet backhaul or they can connect wirelessly. If your home is already wired with Ethernet, you may want to take advantage of these connections to increase the range of your eeros and reduce the risk of wireless interference.
What about eero Beacons?
eero Beacons do not have any Ethernet ports, so they cannot be connected to your network over Ethernet. They can, however, be part of a mixed network of wired and wireless eeros.