In an Ironman id say around 2% breast stroke, its perfectly feasible but as already said unless your a very strong breast stroker its going to take a while, it will also be more tiring.
Ive also been told (not sure if its true or not) that breast stroke can be prone to causing injuries/strain in the groin area.
My advise would be to see a physio, and get some advise re the state of your shoulder and begin learning crawl with coached one to one lessons and see how it goes. Im sure many people before you with dislocated shoulders have managed ok?
Not the same as a dislocation but I broke my elbow 2 years ago (radius bone) It took perhaps 2 months before I had any reasobable movement and then 2-3 months of pyhsio to get movement back, in total it was 6 months before I could fully straighten my arm again. During the physio I was advised to start gently swimming again as this would help my recovery.