Anecdotal, but I've messed around with contrast baths some to help heal finger flexor tendon issues. I must have been keeping the water too cold because the pain was just flat out unbearable for anything more than about 30 seconds. With only my hand submerged to the wrist, I could actually feel the cold blood flowing back up the rest of my arm through the veins. My roommate thoroughly enjoyed watching me try and sit at the couch and deal with how bad it hurt. That said, a couple weeks of sacking up really did seem to help the healing process.
I also have a friend that swears by this method for her hands.. and at first would seem to bounce back REALLY quick from tendon tweaks.. now she just doesnt get them at all, despite being a VERY strong climber on the types of holds that typically hurt other people.