http://www.schutzhund.fsnet.co.uk/Hi dollface, if you go to the above link you will find a list of clubs and contacts. They will be able to tell you if there are currently any DDB in training, although I am not personally aware of any.
THe majority of the dogs participating in this sport in the UK are GSDs, with a few Dobes, Rotts, and Malis,
There are "other" breed individuals such as American Bulldogs etc that are also in training.
The agility requirements for Schutzhund are not so demanding as Working Trials; eg the former only has an A frame, not a 6ft scale nor a 9ft long jump.
Lists of surveys are posted on this site and so it may be worth you visiting as a spectator to talk with enthusiasts to get a better
idea.
As Moonmaiden says you need to have your dog tattood and belong to the BSA and be accepted for training by a club before you are allowed to participate in training activities.
The first rung in the ladder is the BH or Begleithunde which all dogs must pass to demonstrate they possess the temperament and that they are under sufficient control before they may participate in the Sch 1,2,3 competitions.
HTH