Is tendonitis a symptom of carpal tunnel syndrome? Can this be treated?

Maybe and yes. Carpal tunnel syndrome is thought to be caused by the tendons and nerves traveling through the wrist becoming inflamed, putting pressure on the median nerve, causing tingling and numbness in the fingers. This is treated by "releasing" the tendonous band through which this nerve travels. An orthopedist will do this with surgery. A skilled osteopathic can do this with osteopathic manipulation.
Typically not. Unless the tendon involved is one of those that passes through the carpal tunnel, it is unlikely to be associated with carpal tunnel syndrome. Tendinitis can be treated by physical therapy in most cases, although medications can often be helpful if therapy alone does not resolve the symptoms.
No, yes. No,?tendinitis is a different condition than carpal tunnel syndrome, it is not a symptom. Yes, there are many treatments for Tendonitis.