Can Backend Servers Access the Internet Using the EIP of the Load Balancer?

No.

The load balancer uses the EIP to receive requests from the Internet and routes the requests to backend servers over a private network.

If you want the backend servers to access the Internet or provide Internet-accessible services directly, you can bind an EIP to each backend server. You can also configure a NAT gateway for the backend servers so that they can share an EIP to access the Internet.