Hi,
We have the same model nebulizer and did use it on our WDW trip. My DD (3) has severe asthma and we would not be able to travel without a portable nebulizer.
Just make sure when you get the nebulizer to buy the back up battery and the car power adapter (FYI - the nebulizer comes with all the adapter plugs you need for international travel - a big plus for us since we are planning a trip to Thailand). Another attachment you may want to get is the extra tubing attachment (it is specific to this nebulizer), so you do not have to hold the actual unit so close to your child's face. If you use a mask, you need to get the mask that fits with their nebulizer cup also.
Another thing to make sure you have is a new prescription from your pediatrician, in case you run out of medication, saves time at the drugstore with trying to get prescriptions transferred.
We used the nebulizer in the park with the battery, then at night recharged the battery in the hotel room, this worked very well for us. If you do not get the battery, you can go to first aid in all of the parks and plug in your nebulizer.
Hope this is helpful.