Shoulder injuries are fairly common in grappling. Most often they are the result of an overzealous Kimura (chicken wing) or Americana (V arm lock) attack, but shoulders can also get damaged by other techniques, such as throws and sweeps. While it is entirely possible that you may never have a shoulder injury, the odds of someone in your training group getting injured this way are fairly high.
Another sport that has similar injuries to the shoulder is kayaking. In kayaking, especially whitewater kayaking, the arm is often placed into positions that closely resemble the two above-mentioned bent arm locks; these compromised positions can result in both chronic and acute shoulder injuries. The reason I bring up this up is because there are some excellent shoulder rehabilitation resources available for kayaking, perhaps because it is an Olympic sport. Most of this information can be applied directly to rehabilitating grappling shoulder injuries.
The best online layman’s resource for shoulder anatomy and rehabilitation that I know of is a guide produced by the USA Canoe and Kayak Association on shoulder exercises.
The material in this guide is totally applicable to any sport, our own included. Do yourself a favor and save a copy of this document to your hard drive. Hopefully your grappling career will be injury free, but information like this is always useful to have on hand, either for your own use or to forward on to an injured training partner.