This question is perplexing because Ibsen’s Ghosts is, of course, not an Absurdist play, but a key piece in the Modernist, realistic genre of the late 19th-early 20th century  dramatic forms pioneered by Ibsen, Chekhov, and others.  It dealt with the socio-psychological dilemmas of everyday people, dramatizing the conflicts brought on by the rapid changes in social consciousness – women’s rights, manufacturing changes, etc.  Ghosts specifically referred to the “ghosts” of the characters pasts, not to anything unreal.

Absurdist drama, on the other hand, seeks to dramatize the dilemma posed by the philosophical notion that life itself has no larger meaning, that events are not logical but absurd.  It is a philosophical, not a social or psychological, exploration, and as such has no interest in “real characterization”; the characters are spokespersons for the playwrights’ attempts at staging the non-action of human endeavors.  An argument could be made that they are not "dramas" at all, since they do not fulfill Aristotle's definition of drama as "imitation of an action."