It's pretty necessary, but I suppose you could get by without it if you continuously blast them with a humidifier, or constantly mist them, while using an antiwilt. Fresh cuttings don't have roots anymore, so they have to get the required moisture through the leaves, which requires humidity. A humidity dome can be something as simple as a clear Tupperware container, 100 pack CD container, or an extra clear tub the same size as your cloner tub.