It serves no value to the plot. You can however find Zubat there, and with the addition of a mystery gift; mareep, pineco, shuckle, teddiursa, houndour, stantler, and smeargle.
The Mystery Gift Pokémon never made it to the final cut, however. They decided to dump these guys into the Emerald Safari Zone, or in Smeargle's case, Artisan Cave.