I use a regular tree Aussie saddle on my gaited Bashkir Curly X Arab mare, and she does great. I like the Aussie because it allows more air to get through to my horse's back, and it doesnt sit directly on their backbone as a western saddle would. That is the best saddle that we have found for her so far, and it doesnt hinder her movement at all. I am able to ride her gaits better as well, due to the stirrup placement on an Aussie saddle. I feel much more secure and I love using it on the trail.
I suppose if she had more extravigant movement as some other highly gaited breeds it could become a problem, but she is so narrow in the shoulders that she needs a regular tree or else it would be too wide for her.
Shaneequah, 1998 gaited Bashkir CurlyxArab mare
Johnny Cash, 2001 Arab x pony gelding
Brighty, 2013 Standard Donkey jack