Technical term, not widely used in software engineering outside of agent-oriented programming but finds some use. In agent-oriented programming the antonym is depender, though in general usage the common term dependent is used instead. There is no common language equivalent for dependee, however – other metaphors are used instead, such as parent/child. The circumlocutions “A depends on B” and “B is depended on by A” are much more common in general use than “A is the depender, B is the dependee”.
depend + -ee (“target of action”)