my personal opinion: Even though humans don't appear in the TLK movies, there are slight references that they actually DO excist. For example, in TLK2 at the final battle, Timon pretends pumba's tail is a shotgun or some sort of rifle, and looking at the reaction of the freaked-out outsiders, they definately know what guns are, and therefore, had possibly a few dangerous encounters with humans. And besides this, in TLK1 during the ''I can't wait to be king'' song Zazu mention's that he'll leave Africa. Therefore, he has some sense of knowledge about ''geography'' which he possibly somehow learned from humans. So I think humans dont appear in any of the TLK movies NOT because they don't excist, but mainly because they aren't very important and got nothing to do with the plot, but however humans do actually do appear in the Timon and Pumba cartoon/animation (or however it's called). I dont know if this confirms that humans excist in the TLK universe, but well both TLK movies and the Timon and pumba animation are owned by Walt Disney I guess.
So, tell me your opinions please.