Absolutely. With a good instructor and practicing on your own or with a small class size, no one should be beyond pilates, regardless of their body type or fitness level. Trying to keep up with a class, even a beginner level one, might be difficult until you have some more knowledge of the routines, though.

I would recommend starting with an individual session with the instructor who will be teaching the group classes. This way, he or she will know you personally, and the modifications you will need to make in order to make the exercises safe for your shoulder and comfortable for your size, rather than just checking on you through the class.

I have a condition that makes exercise of all kinds very difficult, and when I first started pilates, I had lost a great deal of muscle (3lb weights felt like cinder blocks). The equipment and resistance, as well as just the bodyweight exercises themselves, helped me more than I can express. Before my first session, I sent the instructor an email, explained my needs, and told her that I would like her to approach things more as physical therapy than "getting fit," and she was incredibly understanding and excited to help - I think this might be a good idea for you, as well.

Also, while you are certainly limited in what you can do because of your fitness level and injuries, you can do so much at your weight (this is coming from someone who has gone from a 34 BMI to now 22). Don't let it stop you! I think the doubt about this comes from the fact that it often is absolutely, 100% hard to get started at yoga and pilates when you are heavier (I won't lie, both are much easier with less of yourself in the way), and so we assume that it's just not meant for us - but that's not true. This yogi is outrageously strong and amazing, and also, obese. And no need to worry about flexibility - that comes with practice (and you haven't practiced yet)!

Be kind and patient with yourself; change and healing take time. And feel free to PM me if you need any help! Best of luck - I'm sure you're going to do better than you think.