Which bird species/families worm-dance and is this learned behaviour?
Short answer
Sea gulls indeed tap the ground to surface earth worms, which is known as worm charming. Traditional human societies have practiced a similar technique known as worm grunting, involving vibrating the ground. Worm grunting is obviously a learned behavior passed down for generations in Florida. In other animals, such as gulls, I wasn't able to find evidence whether it is learned or innate behavior. 

Background
From wikipedia:


  Worm charming is especially [observed] among birds. The methods used vary; however, tapping earth
  with feet to generate vibrations is widespread. One common example is
  the "Seagull dance". The wood turtle also seems to be adapted for worm
  charming, as it is known to stamp its feet – a behavior that attracts
  worms to the surface and allows the turtle to prey on them.


It is popular belief says that the charming mimics the drumming vibrations made by rain and that worms are attracted by it. However, studies have indicated that the charm vibrations sound similar to those made by burrowing moles, a voracious worm predator and that the charming behavior of worms surfacing reflects an escape behavior of worms, namely the abandoning of their safe burrows to expose themselves to the real danger once surfaced (Catania, 2008). 

The authors investigated the charming reaction of the worms by studying human-indiced charming, a technique used by fishermen. For generations, many families in and around Florida's Apalachicola National Forest have supported themselves by collecting the large endemic earthworms (Diplocardia mississippiensis). This is accomplished by vibrating a wooden stake driven into the soil, a practice called “worm grunting”. This worm grunting is obviously learned behavior.

However, I couldn't find evidence whether the worm charming in birds and turtles is learned yes or no. 

Reference
- Catania, PLoS ONE 3(10): e3472