Sounds like you are on the right track with strong shoulders. Most common injury for Swimmers as they get older is shoulder problems, which is similar to most overhead sports, so the stronger those shoulders can be the more protected and injury free they will be.
One thing to keep in mind is that you will get the most bang for your buck at improving swim times by improving the power you generate off your turns. A good flip turn and explosive push off the wall is what separates good and great swimmers. So nice strong and powerful squats are of HUGE benefit to swimmers!!!
Probably stuff you already knew, but thought I would throw it out there