The term does not imply a relationship between spanker and spankee other than the act, although such a relationship often exists.
In consensual spanking, the act fulfills needs of the participants. In particular, the spankee may ask to be spanked or may "break a rule" that brings about a spanking. Often the spanker is simply acting out what the spankee wishes for. In contemporary society, it is common that the spanker is performing a role in the spankee's life. This is typical when a male spankee has hired a female spanker (perhaps his Domme).
In French, a spanker is called fesseur. "Frère Fesseur" (Brother Spanker) was the title of a cleric, especially in the Jesuit order, who was specifically charged with the professional administration of spankings on the (typically bared) buttocks of naughty pupils in reputedly strict Catholic schools.
In Spanish, a spanker is called azotador (and a spankee is called azotado).