My experience working in conjunction with "Super" Phyiscal Therapist Scott Heinlein
http://www.lifestrengthpt.com/team taught me enough about the shoulder girdle to know what to do last year when one of my athletes incurred a seemingly spontaneous shoulder injury during practice.  The athlete reported that she "couldn't move" her shoulder, and could hardly climb out of the pool. Even as she stood out of the pool, she reported that her shoulder hurt "to just stand there".  Instead of sending her home with the recommendation of ice and Alieve, I asked her to try a "knee pushup".  She oblidged, and although the first 3 were a bit stiff she was able to feel no pain doing sets of 3, then sets of 5 knee (and then normal style) pushups.  Her shoulder felt better as she completed her sets.  The next day she swam with no pain.

I've learned that movement (proper and normal human movement) is the key to shoulder health --  proper movement, properly timed to occur prior to swimming practice.  I've never been much of a "Static Stetching" coach as it is, but the latest research (really this is 3-5 year old research) shows why "Dynamic Stetching" is the best option for athletes prior to training, as well as racing.  The "dynamic" movement of performing a pushup helped my athlete that day simply because her shoulder was "reset" to its proper spot by performing a basic excercise well.

I believe there is a place for a small bit of static stretching -- but it must be preceeded by warmup-based movements like pushups.  For swimming workouts, T2 Aquatics' Pre-Practice routine is full of pushups and other dynamic activity like medicine ball throws (chest passes and passes between the legs), planks, squats, abs, and cord work. 

Check out Dr. G. John Mullen's website http://www.swimmingscience.net/2012/07/dryland-mistake-stretching-part-ii.html for a great article regarding the dryland mistakes we tend to make as coaches and athletes.  Thanks to Dr. Mullen for providing many insights on this type of issue (and many others) on his outstanding site http://www.swimmingscience.net/ If you are a coach you should really check this out!