Search traffic

Those are two completely different connections from the sound of things. A web service call is not dependent on the method on the front end. As the "frontend server" is acting as a client to the "backend server", it would be dictated by the config of the two server (or VIPs, whatever is terminating the call from the front end server). The frontend server is initiating the call (HTTP or HTTPS), but the back end server might redirect etc.

Long and short, how the client and server are configured (in this case the client is the front end server) will dictate the connection.