I have used dressage to train my TWH. There are some tests adapted to the WH, some shows are allowing them. Many gaited horse shows are adding them.
I live in AK so I just show up where ever I want to ride my guy, admittedly not at a dressage show yet until I know we are doing excellent.
Here are tests from intro to third level National Walking Horse Association
I love the responsiveness and strength my horse is building. I love the way dressage training builds one skill that leads into another. It is a slower process but it has been a great way of going for us!