Here you can read up on the helper classifications:
United Schutzhund Clubs of America - Education
You can click on the individual categories and you will see a short description.
Just because a helper is classified for a certain level (club, regional, national; that means at which level they can be trial helpers), does not automatically make them a good training helper, i.e. a helper that can help you train you and your dog.
As far as bringing your dog along, I would follow their guidelines. Usually dogs are in the car in crates while other dogs are being worked. You will have to follow "club rules" for that.
I would definitely also check out the club that has Dobes. It does not mean it is the better club, but I would find that intriguing simply to go and watch them train.