Yes, there are several boarding schools outstanding equestrian programs in USA. Applying to these boarding schools still requires your son to submit Test scores such as SSAT/TOEFL with excellent GPA. As you might know, Chinese applicants to those boarding schools continue to face severe competitions even though your son's experience with equestrian program will definitely help.
Some of top universities such as Colgate, Standford, Smith, USC, Princeton, UPenn and Washington University have very competitive equestrian programs and always look for students like your son. I recommend you to search which boarding schools has strong ties with these universities and success with state and national competition as well. Choosing a school with strong success history of equestrian program would be one of most important criteria when your applies to boarding schools if you hope you son continue to participate in this wonderful field.