By the RAW, it's absolutely possible.
But it's bad for both flavor and balance. Flavor, because why does enemy A moving away from you allow you an extra attack on enemy B, whose just standing their defending? Think how annoyed you'd be as a player if this happened to you because an NPC did something stupid. Balance, because you can get extra, full BAB attacks on a powerful creature by cleaving through his minions. (Or, in the most munchkiny of cases, a bag of rats held for the occasion.)
The idea that you can only cleave onto people who also provoke an AoO is attractive, but I'm not sure how that would work in practice. (Do you delay the cleave until a later initiative? Or is it only useful against foes acting in unison?)