Hi luvlatin
You mentioned judges in your comment, so i guess you're referring to aspiring competitve dancers. you're right in saying that exercises to improve mobility of the trunk (turning etc) can be a problem for the back. However, competitive dancers have presumably been dancing to some level for a few years, and this might give them reasonable mobility to start from. I would recommend getting advice from a good physiotherapist. I'm blessed with very good flexibilty, but on the odd occasion have injured my back (doing other things) and have found to my delight that dancing, with its combination of movement and good posture, has considerably helped my recovery. So i would imagine that with some care, and being certain of maintaining good posture at all times, it must be possible to improve mobility safely. Also, remember that strong abdominal muscles are a pre-requisite for good back care.