Thank you for taking such good care of him. You probably take better care of Vegas then some people who have had them for years do.
If he is swimming wonky maybe swim bladder disease? I believe feeding peas can help (do some googling as I have no experience with SBD).
If it is in fact dropsy you can tell by looking at him from above. Are his scales sticking out? If yes it is dropsy. Unfortunately there is no cure for dropsy.
It is most likely SBD, but dont just feed him a raw pea as this is not good for them. I think it has to be thawed. I've only fed spinach to my fish as the bag of pea we use as an ice pack at softball games. :) Not becoming my fishes dinner.
I hope all goes well. Your are a very, VERY caring owner. Hate to admit it, but you have gone to greater lengths for one betta forced into your care then I have ever gone to for my fish. Your should be proud of yourself.