Creo que se trata de que son empleados cuyo trabajo no es de cara al público (clientes). Sin embargo están perfectamente coordinados con el resto de los departamentos.

ACEPCIÓN PRIMERA:

back end
Definitions (2)

1. General: 'Behind the scene' operations center of a business with which the customer rarely comes in contact. Back-end offices or departments provide the services that make up a business function, such as accounting, administration, communications data processing, document handling. See also front end.

2. Network marketing: Commission received by an independent agent on the sales revenue of the agents recruited by him or her (agent's downline).


http://www.businessdictionary.com/definition/back-end.html

INTERFACE: aCEPCIÓN 2

v.intr.
1. To serve as an interface or become interfaced.
2. To interact or coordinate smoothly: "Theatergoers were lured out of their seats and interfaced with the scenery" (New York Times).

http://www.thefreedictionary.com/interface