Is there any evidence for some people to be more prone to tendonitis than others?

Yes. A multitude of things can make someone more prone to tendonitis including genetic predisposition, repetitive activities associated with work or play, boney abnormalities, tendon contractors, etc.
Soft tissue. Disorders are affected by general health so yes . If you are hypothyroid, have gout have a baseline inflamm disorder have fibromyalgia etc so yes.