It all depends on how many people are online, and who they are. Several people already have creeper farms. So when they come on, they make up most of the worlds creeper cap. Which makes exploring at night easier. But finding creepers for gunpowder, a little harder. Otherwise, yes. Ordinarily has good rates. Assuming you've lit up 128 block perimeter around the farm. So the only thing that can spawn Near you is creepers.