I have used those lights before and they don't really produce the same effect. First off they do not produce much light at all. At best they simulate the look of a candle but really do not have enough light to provide much of an effect through a diffuser.There are controllers that are designed specifically for this purpose and as already stated that is most likely what WDW uses. However - there are also individual bulbs that you and I and anyone else can purchase that will flicker.
No special wiring, no special electronics - just a special light bulb that produces the flicker effect.
http://www.lightbulbsdirect.com/page/001/CTGY/Dec+Flicker
A couple of years ago I was trying to get that gas lamp flicker effect in a bunch of plastic jack-o-lanterns I put out for Halloween. My first idea was to use the flicker bulbs but they did not produce enough light to illuminate them and the light was more constant than the dim to bright effect I wanted.