Yes I think that sophrology is very great for riders.
It allows people to be more conscious on the pressure points and the slackening ones, the weight distribution, identifying the emotions such as stress, and also being focused on the present moment.
It is very useful if you want to improve your focus, the management of your emotions, the outline of a show, your breathing and also your performances (by positive view).
It is also a way to avoid irritation which can be good in horse riding for any riders.
We used to make sessions every week, twice a week during a month before going to a national championship and everybody in my club felt less pressure concerning this event :)