When a horse is in rehab you do what you can to help the horse recover from their injury and return to full athletic function as you would a human athlete: physical therapy, conditioning, hyperbaric oxygen, etc. I do lots of therapeutic massage and manipulative techniques on horses to help improve their athletic performance.
"Hormones and no-no drugs" is a broad, open statement that really doesn't mean anything. Many drugs are beneficial and good for the horse, are essential to excellent quality veterinary practice, and are used for the health and wellness of the animal on a daily basis at the track, but are not allowed on race day.
"How long do they last, can they be tested for". Yes. You might want to review the Racing Medication and Testing Consortium regulations, FAQ's and site and familiarize yourself with therapeutic medications, use and withdrawal times here
http://www.rmtcnet.com/
And go to TheHorse.com and sign up free, then enter "rehabilitation" and "raceday medications" to learn more about it.